Alkali source and/or sink using ion-conducting solid electrolyte and mixed ion-electron conductor electrode

Abstract

Some variations provide an alkali metal or alkaline earth metal atom source (e.g., vapor cell) with a solid ionic conductor and a mixed ion-electron conductor electrode. Mixed ion-electron conductor electrodes are used as efficient sources and/or as sinks for alkali metal or alkaline earth metal atoms, thus enabling electrical control over metal atom content in the vapor cell. Some variations provide a vapor-cell system comprising: a vapor-cell region configured to allow a vapor-cell optical path into a vapor-cell vapor phase; a first electrode containing an mixed ion-electron conductor that is conductive for an ion of at least one element selected from Rb, Cs, Na, K, or Sr; a second electrode electrically isolated from the first electrode; and an ion-conducting layer between the first electrode and the second electrode. The ion-conducting layer is ionically conductive for at least one ionic species selected from Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, or Sr.sup.2+.

Claims

1. An atom-source system arranged to supply atoms for measurements, said system comprising: a first electrode disposed in contact with a vapor-cell region, wherein said first electrode contains a first mixed ion-electron conductor; a second electrode that is electrically isolated from said first electrode; and an ion-conducting layer interposed between said first electrode and said second electrode, wherein said ion-conducting layer is in ionic communication with said second electrode.

2. The atom-source system of claim 1, wherein said atom-source system is a vapor-cell system comprising said vapor-cell region configured to allow at least one vapor-cell optical path into a vapor-cell vapor phase within said vapor-cell region.

3. The atom-source system of claim 1, wherein said ion-conducting layer is ionically conductive for at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+.

4. The atom-source system of claim 1, wherein said first mixed ion-electron conductor is selected from the group consisting of alkali monoferrites, alkali monoaluminates, alkali monogallates, and combinations thereof.

5. The atom-source system of claim 4, wherein said first mixed ion-electron conductor is doped with one or more atoms selected from the group consisting of Pb, Cd, Ca, P, V, Nb, Ta, Si, Ti, Ge, and combinations thereof.

6. The atom-source system of claim 1, wherein said first mixed ion-electron conductor is selected from alkali pyrophosphates.

7. The atom-source system of claim 6, wherein said first mixed ion-electron conductor is doped with one or more atoms selected from the group consisting of Ca, Sr, Ba, Pb, Y, La, Nd, and combinations thereof.

8. The atom-source system of claim 1, wherein said first mixed ion-electron conductor is conductive for at least one element selected from the group consisting of Rb, Cs, Na, K, and Sr.

9. The atom-source system of claim 3, wherein said ion-conducting layer contains said at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+.

10. The atom-source system of claim 9, wherein said first mixed ion-electron conductor includes said at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+.

11. The atom-source system of claim 2, wherein said vapor-cell region contains a vapor phase comprising metal atoms that are included, in ionized form, in said first mixed ion-electron conductor.

12. The atom-source system of claim 11, wherein said metal atoms are selected from the group consisting of Rb, Cs, Na, K, Sr, and combinations thereof, wherein said ion-conducting layer contains at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+, and wherein said metal atoms are the same element as said at least one ionic species.

13. The atom-source system of claim 1, wherein said ion-conducting layer comprises a material selected from the group consisting of -alumina, -alumina, yttria-stabilized zirconia, and combinations thereof.

14. The atom-source system of claim 1, wherein said ion-conducting layer comprises a material selected from the group consisting of NASICON, LISICON, KSICON, chalcogenide glasses, and combinations thereof.

15. The atom-source system of claim 1, wherein said second electrode contains a second mixed ion-electron conductor.

16. The atom-source system of claim 15, wherein said second mixed ion-electron conductor is selected from the group consisting of alkali monoferrites, alkali monoaluminates, alkali monogallates, and combinations thereof, optionally doped with one or more atoms selected from the group consisting of Pb, Cd, Ca, P, V, Nb, Ta, Si, Ti, and Ge.

17. The atom-source system of claim 15, wherein said second mixed ion-electron conductor is selected from alkali pyrophosphates, optionally doped with one or more atoms selected from the group consisting of Ca, Sr, Ba, Pb, Y, La, and Nd.

18. The atom-source system of claim 1, wherein said second electrode contains an intercalable compound.

19. The atom-source system of claim 18, wherein said intercalable compound is a carbonaceous material selected from the group consisting of graphite, graphene, holey graphene, graphene platelets, carbon nanotubes, fullerenes, activated carbon, coke, pitch coke, petroleum coke, carbon black, amorphous carbon, glassy carbon, pyrolyzed carbon-containing molecules, pyrolyzed parylene, polyaromatic hydrocarbons, and combinations thereof.

20. The atom-source system of claim 18, wherein said intercalable compound is a transition-metal oxide, a transition-metal dichalcogenide, or a combination thereof.

21. The atom-source system of claim 18, wherein said intercalable compound is intercalative for at least one element selected from the group consisting of Rb, Cs, Na, K, and Sr.

22. The atom-source system of claim 1, wherein said second electrode is in contact with a reservoir region containing alkali or alkaline earth metal atoms.

23. The atom-source system of claim 1, said system further comprising electrical traces physically located on, but electrically insulated from, said ion-conducting layer.

24. The atom-source system of claim 1, wherein said atom-source system further includes a heater attached to, or in thermal or electromagnetic communication with, said atom-source system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a schematic of an exemplary vapor cell, in some embodiments, with a single-layer mixed ion-electron conductor layer first (front) electrode disposed in contact with the vapor-cell region.

(2) FIG. 1B is a schematic of an exemplary vapor cell, identical to FIG. 1A, except that laser beams are not shown.

(3) FIG. 2 is a schematic of an exemplary vapor cell, in some embodiments, with a dual-layer first (front) electrode (mixed ion-electron conductor layer and porous electrically conductive layer) and a dual-layer second (back) electrode (mixed ion-electron conductor layer and porous electrically conductive layer).

(4) FIG. 3 is a schematic of an exemplary vapor cell, in some embodiments, with two pairs of electrodes, in region A and region B.

(5) FIG. 4 is a schematic of an exemplary vapor cell, in some embodiments, with a reservoir combined with a second electrode that includes a thick intercalable-compound layer (e.g., graphite layer).

(6) FIG. 5 is a schematic of an exemplary vapor cell, in some embodiments, with a reservoir combined with a second electrode that includes a thick intercalable-compound layer and two pairs of electrodes (region A and region B).

(7) FIG. 6 is a plan-view schematic of a dual-layer electrode disposed on an ion-conducting layer, in some embodiments.

(8) FIG. 7 is a plan-view schematic of a chip-scale variation of the invention, in some embodiments.

(9) FIG. 8 is a side-view schematic of a chip-scale variation of invention, in some embodiments.

(10) FIG. 9 is a schematic of the invention, in some embodiments, integrated with an atom chip at the package level.

(11) FIG. 10 is a schematic of the invention, in some embodiments, with an atom chip heterogeneously integrated with the solid electrolyte ion-conductor.

(12) FIG. 11 is a schematic of the invention, in some embodiments, with an atom chip fully integrated with one of solid electrolyte ion conductor.

(13) FIG. 12 is a plan-view schematic of electrodes and atom chip wires on an ion conductor in some embodiments of this invention, with an atom chip fully integrated with the ion conductor.

(14) FIG. 13 is an exemplary schematic of a method (process flowchart) of the invention, according to some embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(15) The structures, systems, and methods of the present invention will be described in detail by reference to various non-limiting embodiments.

(16) This description will enable one skilled in the art to make and use the invention, and it describes several embodiments, adaptations, variations, alternatives, and uses of the invention. These and other embodiments, features, and advantages of the present invention will become more apparent to those skilled in the art when taken with reference to the following detailed description of the invention in conjunction with the accompanying drawings.

(17) As used in this specification and the appended claims, the singular forms a, an, and the include plural referents unless the context clearly indicates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs.

(18) Unless otherwise indicated, all numbers expressing conditions, concentrations, dimensions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term about. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending at least upon a specific analytical technique.

(19) The term comprising, which is synonymous with including, containing, or characterized by is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. Comprising is a term of art used in claim language which means that the named claim elements are essential, but other claim elements may be added and still form a construct within the scope of the claim.

(20) As used herein, the phrase consisting of excludes any element, step, or ingredient not specified in the claim. When the phrase consists of (or variations thereof) appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase consisting essentially of limits the scope of a claim to the specified elements or method steps, plus those that do not materially affect the basis and novel characteristic(s) of the claimed subject matter.

(21) With respect to the terms comprising, consisting of, and consisting essentially of, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus in some embodiments not otherwise explicitly recited, any instance of comprising may be replaced by consisting of or, alternatively, by consisting essentially of.

(22) Some variations of the invention provide an atom-source system arranged to supply atoms for measurements, the system comprising:

(23) a first electrode disposed in contact with the vapor-cell region, wherein the first electrode contains a first mixed ion-electron conductor;

(24) a second electrode that is electrically isolated from the first electrode; and

(25) an ion-conducting layer interposed between the first electrode and the second electrode, wherein the ion-conducting layer is in ionic communication with the second electrode.

(26) As intended herein, an atom-source system is a system arranged to supply multiple cold atoms within a device or confined region for the purposes of one or more measurements based on those atoms. Note that measurements shall be broadly construed to include any application (i.e., system, device, or method) which utilizes or is capable of utilizing a source of atoms, two electrodes, and an ion-conducting layer between the electrodes.

(27) The atom-source system may be, or be contained within, a vapor cell, a cold atom system, an atom chip, an atom gyroscope, an atomic clock, a communication system switch or buffer, a single-photon generator or detector, a gas-phase atom sensor, a nonlinear frequency generator, a precision spectroscopy instrument, an accelerometer, a gyroscope, an atom interferometer, a magneto-optical trap, an atomic-cloud imaging apparatus, or an atom dispenser system, for example. The present invention is expressly not limited to vapor cells. However, the disclosure and drawings will describe vapor cells as exemplary embodiments for illustration purposes, with the understanding that the principles of the invention may be applied to a variety of other atom sources and atom-source systems.

(28) In some embodiments, the atom-source system is a vapor-cell system comprising a vapor-cell region configured to allow at least one vapor-cell optical path into a vapor-cell vapor phase within the vapor-cell region. The ion-conducting layer may be ionically conductive for at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+, for example.

(29) Certain variations of this invention are premised on an alkali metal or alkaline earth metal vapor cell with a solid electrolyte ionic conductor (e.g. beta-alumina) and at least one mixed ion-electron conductor electrode. The mixed ion-electron conductor electrodes are used as sources and/or as sinks for alkali metal or alkaline earth metal atoms, thus enabling electrical control over alkali or alkaline earth content of the vapor cell. The mixed ion-electron conductor electrodes enable orders-of-magnitude enhanced alkali or alkaline earth metal flux.

(30) A mixed ion-electron conductor means a material having both electrical conductivity greater than 10.sup.10 S/cm, preferably greater than 10.sup.6 S/cm, and ionic conductivity greater than 10.sup.10 S/cm, preferably greater than 10.sup.6 S/cm. Note that MIEC is used interchangeably herein with mixed ion-electron conductor.

(31) Previous devices proposed for controlling alkali vapor pressure using solid electrolytes have employed inert electrodes, typically as interconnected platinum lines. The electrochemical reaction in such devices requires the transport of three distinct species (alkali ions, electrons, and alkali neutral atoms), each of which can transport only in one of three layers (the solid electrolyte, the electrode, and the vapor phase, respectively). The electrochemical reaction can only occur at edges of the inert electrode lines where these three phases meet. Because surface diffusion of alkali metals is slow at typical alkali vapor cell temperatures (e.g. for atomic clocks and gyroscopes), the actual active area of a device is orders of magnitude less than the area of the solid electrolyte.

(32) By contrast, mixed ion-electron conductor electrodes conduct both electrons and alkali ions. By using a blanket mixed ion-electron conductor electrode, for example, the electrochemical reaction occurs across a plane instead of at a line, thus allowing substantially more of the electrolyte surface to be actively involved in the reaction. This results in orders-of-magnitude faster alkali vapor sourcing and sinking performance.

(33) The primary purpose of this invention is to directly and precisely control the vapor pressure of alkali atoms or other metal atoms within an atom-source system. Electrical inputs enable controlled dosing of metal atoms (e.g., alkali atoms) into and out of a vapor cell or other atom source. The ability to control the vapor pressure of atoms has multiple measurement applications, mainly related to atomic physics.

(34) For instance, the ability to control the vapor pressure of alkali atoms can enable long population lifetimes of cold atoms, particularly in miniaturized atomic systems. Cold atoms (such as at temperatures of about 1 K to about 1 K, typically from about 100 K to about 1000 K) are useful for precision timing and navigation applications. In certain applications, cold atoms can be made that are in the nanokelvin range or even less (10.sup.9 K).

(35) Cold atoms are typically formed from a subset of warmer atoms inside a vapor cell, e.g. through trapping and cooling in a magneto-optical trap (MOT). The time constant of the cold-atom population depends on the density of other atoms in the vapor cell because of collisional heating. For fast loading (i.e. short time constant on loading), it is desirable to have a high vapor density of atoms. However, for highly stable and highly precise measurement, it is desirable to have the population of cold atoms last as long as possible. Therefore it is desirable to have a long time constant and low vapor density once the population of cold atoms has been cooled and trapped. The active control of the vapor density in a vapor cell, provided in this patent application, enables a fast loading time as well as a long lifetime.

(36) Additionally, the ability to source alkali atoms with low power and with the emission of no other chemical species is desirable. Conventional alkali dispenser sources require high currents (5 A is typical) and high power (e.g., Societ Apparecchi Electrici e Scientifici (SAES) Getters, Milan, Italy). For portable battery-powered atomic clock applications, a power budget of watts will yield device lifetimes so short as to be impractical. Furthermore, alkali dispenser sources emit non-alkali gases in their initial period of operation. For a system connected to a vacuum pump, this is often not a concern, However, for portable atomic physics systems that are infrequently or never serviced, non-alkali gases can shift or broaden the atomic transition frequency and/or increase the vapor cell pressure high enough to prevent the formation of a population of cold atoms.

(37) Variations of this invention enable active, bidirectional control of alkali metal and alkaline earth metal vapor pressure within a vapor cell. This invention is applicable to portable and highly-precise position, navigation, and timing systems. Further, combining this invention with atom chips having dynamic control of vapor pressure allows device miniaturization.

(38) For convenience, alkali or alkali metal may be used in this specification to refer to one or more alkali metals, one or more alkaline earth metals, or a combination thereof. Alkali metals include Li, Na, K, Cs, Rb, or Fr. Alkaline earth metal include Be, Mg, Ca, Sr, Ba, and Ra.

(39) Also, source, sink, source and/or sink, source/sink or the like may be used herein to refer to a source of alkali metals and/or alkaline earth metals; a sink of alkali metals and/or alkaline earth metals; or a material or structure that acts as either a source or sink of alkali metals and/or alkaline earth metals, depending on local conditions (e.g., temperature, pressure, or electrical potential), concentrations of species, etc.

(40) Within the vapor chamber volume, the vapor chamber contains an atomic vapor, preferably that of an alkali metal or an alkaline earth metal. The atomic vapor may generally contain any atomic metal, including mercury (Hg) or rare earth metals (e.g., Yb, Ce, Nd, Sc, or Y).

(41) Optionally, the atomic vapor is isotopically enriched or purified. When the alkali or alkaline earth metal is isotopically enriched, the relative abundance of the isotopes of a given element are altered, thus producing a form of the element that has been enriched in one particular isotope and depleted in its other isotopic forms. The alkali or alkaline earth metal may be isotopically pure, which means it is composed entirely of one isotope of the selected alkali or alkaline earth metal.

(42) In some embodiments, the vapor chamber contains nothing but the atomic vapor as a rarefied gas, i.e. the vapor chamber is under partial vacuum.

(43) In other embodiments, the vapor chamber contains additional gases in addition to the atomic vapor. Additional gases may be selected from N.sub.2, CH.sub.4, He, Ar, Ne, Xe, NH.sub.3, CO.sub.2, H.sub.2O, H.sub.2, or mixtures of these or other molecules, for example. Non-metal atoms (e.g., elemental H, N, or O) may also be used as additional gases. The other gas or gases may be used as a buffer gas or as spin exchange gas, for example. Optionally, the other gas or gases may be isotopically enriched or purified. Any additional gas is preferably not reactive with the alkali or alkaline earth metal.

(44) The vapor chamber may be hermetically sealed. The vapor chamber may also be configured in fluid communication with a larger system, which may or may not be collectively (with the vapor chamber) hermetically sealed. The larger system, for example, could be part of a high-vacuum system containing pumps, pressure/vacuum gauges, atom dispensers, getters, getter pumps, getter sources, pill sources, etc.

(45) One or more walls of the vapor chamber volume are at least partially transparent, and preferably substantially transparent, at relevant wavelengths such that there is at least one optical path through the vapor cell volume. It is preferred that the optical path(s) go through the vapor cell, that is, from one wall to another wall. In some embodiments, a laser beam may enter the vapor cell, reflect off a mirrored surface inside the cell, and leave the cell through the same side that it entered.

(46) An optical path is the path of a spectroscopic probing beam of light (or other type of laser beam) into the alkali or alkaline earth vapor-cell region, or in some cases, into a reservoir region. The optical path is optional in the sense that the device itself does not inherently include the beam of light, while operation of the device will at least periodically mean that an optical path is traversing into or through the alkali or alkaline earth vapor-cell region. Also note that an optical path is not necessarily a straight line. Internal reflectors may be included in the system, so that optical reflection occurs. In that case, the optical beam could enter and exit along the same wall (detection probe on the same side as the laser source), for example.

(47) Walls enclose the vapor-cell region, sealing it from the ambient environment. The walls may be fabricated from silicon, SiO.sub.2, fused silica, quartz, pyrex, metals, dielectrics, or a combination thereof, for example. At least one of the walls includes a substantially transparent portion such that there is an optical path through the vapor-cell region. A wall can be made transparent either by fabricating from an optically transparent material, or by including an optical window in a part of the wall.

(48) Some variations provide a vapor-cell system comprising:

(49) a vapor-cell region configured to allow at least one vapor-cell optical path into a vapor-cell vapor phase within the vapor-cell region;

(50) at least one first electrode disposed in contact with the vapor-cell region, wherein the first electrode contains a first mixed ion-electron conductor that is preferably ionically conductive for at least one element (in ionic form) selected from the group consisting of Rb, Cs, Na, K, and Sr;

(51) at least one second electrode that is electrically isolated from the first electrode; and

(52) an ion-conducting layer interposed between the first electrode and the second electrode, wherein the ion-conducting layer is in ionic communication with the second electrode, and wherein the ion-conducting layer is ionically conductive for at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+.

(53) By electrically isolated it is meant that the second electrode is not in direct electrical contact with the first electrode, but electrical communication is possible through an external circuit. Also, the first and second electrodes preferably are not electron-connected nor hole-connected, but are ion-connected, via the ion-conducting layer.

(54) By ionic communication between the ion-conducting layer and the second electrode, it is meant that ions, or their neutral forms, are capable of being transported between the ion-conducting layer and the second electrode. Note that in some embodiments, ions (i.e. positively or negatively charged atoms) may be neutralized at the interface between the ion-conducting layer and the second electrode, so that ions (e.g., as Rb.sup.+ or Na.sup.+) do not leave the ion-conducting layer. In these embodiments, neutralized forms of the ions (e.g., Rb or Na) are transported away from the ion-conducting layer.

(55) The first electrode is in contact with both the ion-conducting layer and the vapor chamber volume. Both the first electrode and the ion-conducting layer may form part of the inner walls of the vapor chamber. The first electrode preferably has a high diffusivity for alkali and/or alkaline earth metal atoms (or other atoms in the vapor cell). This diffusivity includes ionic conduction and any other mass-transport mechanisms that may be involved. The atoms in the atomic vapor have a diffusivity in the first electrode that is preferably at least 10.sup.10 cm.sup.2/s and more preferably at least 10.sup.6 cm.sup.2/s at the device operation temperature (e.g., 25 C.). In various embodiments, atoms in the atomic vapor have a diffusivity in the first electrode of about 10.sup.8 cm.sup.2/s, 10.sup.7 cm.sup.2/s, 10.sup.6 cm.sup.2/s, 10.sup.5 cm.sup.2/s, 10.sup.4 cm.sup.2/s, or higher.

(56) The first electrode is preferably characterized by an electrical sheet resistance of less than about 10 M/square, more preferably less than about 100 k/square, and most preferably less than about 1 k/square, measured at 25 C. The electrical resistivity of the first electrode is preferably less than about 100 k.Math.cm, more preferably less than about 10 k.Math.cm, and most preferably less than about 0.1 k.Math.cm (100 .Math.cm), measured at 25 C.

(57) The first electrode is also preferably characterized by an ionic conductivity of at least about 10.sup.10.sup.1.Math.cm.sup.1, more preferably at least about 10.sup.8.sup.1.Math.cm.sup.1, and most preferably at least about 10.sup.6.sup.1.Math.cm.sup., measured at 25 C. (note that the units .sup.1.Math.cm.sup.1 are the same as S/cm). The ionic conductance (through the electrode thickness) of the first electrode is preferably less than about 10 k, more preferably less than about 1 k, and most preferably less than about 0.1 k (100), measured at 25 C.

(58) The first electrode may include various mixed ion-electron conductor materials. For example, the mixed ion-electron conductor material may be selected from the group consisting of alkali monoferrites (e.g. RbFeO.sub.2, CsFeO.sub.2, etc.), alkali monoaluminates (e.g. RbAlO.sub.2, CsAlO.sub.2, etc.), alkali monogallates (e.g. RbGaO.sub.2, CsGaO.sub.2, etc.), and combinations thereof. Any of these alkali monoferrites, alkali monoalluminates, or alkali monogallates are optionally doped with one or more atoms selected from Pb, Cd, Ca, P, V, Nb, Ta, Si, Ti, and/or Ge, for example. Exemplary compounds for the ion-electron conductor include, but are not limited to, Rb.sub.1-2xM.sub.xAlO.sub.2 (x is from 0 to less than 0.5) wherein M=Pb, Cd, and/or Ca; Rb.sub.2-2xFe.sub.2-xM.sub.xO.sub.4 (x is from 0 to 1) wherein M=P, V, Nb and/or Ta; Rb.sub.2-2xGa.sub.2-xM.sub.xO.sub.4 (x is from 0 to 1) wherein M=P, V, Nb and/or Ta; Rb.sub.2-2xAl.sub.2-xM.sub.xO.sub.4 wherein M=P, V, Nb and/or Ta; and Rb.sub.1-xAl.sub.1-xM.sub.xO.sub.2 (x is from 0 to less than 1) wherein M=Si, Ti, and/or Ge.

(59) In some embodiments, the mixed ion-electron conductor material may be selected from alkali pyrophosphates, such as Rb.sub.4P.sub.2O.sub.7. The alkali pyrophosphate is optionally doped with one or more atoms selected from Ca, Sr, Ba, Pb, Y, La, and/or Nd, for example. Exemplary compounds for the ion-electron conductor include, but are not limited to, Rb.sub.4-2xM.sub.xP.sub.2O.sub.7 (x is from 0 to less than 2) wherein M=Ca, Sr, Ba, and/or Pb; and Rb.sub.3-3xM.sub.xPO.sub.4 (x is from 0 to less than 1) wherein M=Y, La, and/or Nd.

(60) The first electrode may be a uniform layer (e.g., FIG. 1A) or a non-uniform layer. The thickness of the first electrode is preferably less than 500 m and more preferably less than 100 m. In various embodiments, the thickness of the first electrode is about 1 nm, 10 nm, 100 nm, 1 m, 10 m, 100 m, 500 m, or more.

(61) The first electrode may also comprise a region and/or layer with high electrical conductivity, to minimize electrical sheet resistance of the first electrode. For example, the first electrode may include two layersa layer that is substantially a mixed ion-electron conductor and a layer that is a porous, highly electrically conductive layer. The highly electrically conductive layer preferably has an electrical resistivity less than 10.sup.3 .Math.cm, more preferably less than 10.sup.4 .Math.cm, measured at 25 C. In various embodiments in which a porous, highly electrically conductive layer is present, the electrical resistivity of the highly electrically conductive layer is about, or less than about, 10.sup.2 .Math.cm, 10.sup.3 .Math.cm, 10.sup.4 .Math.cm, 10.sup.5 .Math.cm, or 10.sup.6 .Math.cm, measured at 25 C.

(62) The optional porous, highly electrically conductive layer may be a thin (e.g., less than 200 nm) Pt mesh. This may allow the desirable property that an electrical potential, when applied, does not vary considerably (e.g., <0.1 V) across the electrode surface even if the MIEC material has mediocre electrical conductivity or if the MIEC material is very thin. Other exemplary materials for the optional porous, highly electrically conductive layer include, but are not limited to, Mo, W, and Al. The highly electrically conductive layer may also include more than one layer, such as a Ti adhesion layer and a Pt layer.

(63) The optional highly electrically conductive layer preferably does not chemically interact with the ionic species. That is, the highly electrically conductive layer preferably does not form an intermetallic phase and does not chemically react with the ionic species. The optional highly electrically conductive layer preferably does not chemically interact with the ion-conducting layer; portions of the first electrode should not form mobile ions within ion-conducting layer.

(64) In various embodiments, the optional highly electrically conductive layer may be in contact with the ion-conducting layer, in contact with the vapor chamber volume, in contact with both the ion-conducting layer and the vapor chamber volume, or in contact with neither the ion-conducting layer nor the vapor chamber volume.

(65) The first electrode may be designed to have a large amount of three-phase contact length or interfacial contact area. The three phases are electrode, ionic conductor, and atomic vapor. Configurations that may accomplish high three-phase contact include a high-density mesh or grid pattern, a porous material with an open porosity, a high-density parallel line pattern, or a nanowire array, for example. Some of these configurations (e.g., mesh pattern) are enabled by including the highly electrically conductive layer, while other configurations (e.g., porous material or nanowires) may be accomplished with the MIEC material alone. In some embodiments, an electrode is in the form of a solid film, not a porous film with holes.

(66) The ion-conducting layer preferably has high ionic conductivity for an ionic species. The ionic species is preferably an ion of the atomic vapor in the vapor cell. The ionic species is preferably an alkali metal or alkaline earth metal ion, such as (but not limited to) one or more of Na.sup.+, K.sup.+, Rb.sup.+, Cs.sup.+, or Sr.sup.2+. In certain embodiments, the ionic species is an ion of another metal, such as Hg.sup.2+.

(67) The ionic conductivity of the ion-conducting layer, measured at 25 C., is preferably about 10.sup.9 S/cm or higher, more preferably about 10.sup.6 S/cm or higher. In various embodiments, the ionic conductivity of the ion-conducting layer at 25 C. is about 10.sup.8 S/cm, 10.sup.7 S/cm, 10.sup.6 S/cm, 10.sup.5 S/cm, 10.sup.4 S/cm, 10.sup.3 S/cm, or 10.sup.2 S/cm.

(68) The ion-conducting layer is preferably a solid electrolyte. For example, the ion-conducting layer may be a large fraction (>50% by weight) -alumina, -alumina, or a combination of -alumina and -alumina. -alumina and -alumina are good conductors of their mobile ions yet allows negligible non-ionic (i.e., electronic) conductivity. -alumina is a hard polycrystalline or monocrystalline ceramic which, when prepared as an electrolyte, is complexed with a mobile ion, such as Na.sup.+, K.sup.+, Li.sup.+, or an ionic version of the alkali or alkaline earth metal. -alumina and/or -alumina are also referred to herein as beta-alumina. Beta-alumina solid electrolyte is a fast ion-conductor material used as a membrane in several types of electrochemical cells. Beta-alumina and other hygroscopic ionic conductors preferably do not contact humid air.

(69) Other possible solid electrolyte materials for the ion-conducting layer include yttria-stabilized zirconia, NASICON, LISICON, KSICON, alkali-ion-exchanged versions thereof, and combinations of any of the foregoing. In these or other embodiments, chalcogenide glasses may be used as solid electrolyte materials for the ion-conducting layer. Exemplary chalcogenide glasses include, but are not limited to, RbIGeSe.sub.2Ga.sub.2Ge.sub.3 and CsIGeSe.sub.2Ga.sub.2Ge.sub.3.

(70) The second (back) electrode must not be in direct electrical contact with the first electrode. The second electrode is in direct or indirect contact with the ion-conducting layer. The second electrode is typically not in physical contact with the vapor-cell region. Optionally, the second electrode is in contact with a reservoir region containing alkali or alkaline earth metal atoms, or other metal atoms. Each electrode is typically connected to an electrical lead.

(71) The second electrode may be fabricated from common electrode materials including, but not limited to, Pt, Mo, W, Ni, Cu, Fe, and Al. The second electrode may be solid or porous.

(72) In some embodiments, the second electrode is also a mixed ion-electron conductor. The second electrode may include various mixed ion-electron conductor materials. For example, the mixed ion-electron conductor material may be selected from the group consisting of alkali monoferrites (e.g. RbFeO.sub.2, CsFeO.sub.2, etc.), alkali monoaluminates (e.g. RbAlO.sub.2, CsAlO.sub.2, etc.), alkali monogallates (e.g. RbGaO.sub.2, CsGaO.sub.2, etc.), and combinations thereof. Any of these alkali monoferrites, alkali monoalluminates, or alkali monogallates are optionally doped with one or more atoms selected from Pb, Cd, Ca, P, V, Nb, Ta, Si, Ti, and/or Ge, for example. Exemplary compounds for the ion-electron conductor of the second electrode include, but are not limited to, Rb.sub.1-2xM.sub.xAlO.sub.2 (x is from 0 to less than 0.5) wherein M=Pb, Cd, and/or Ca; Rb.sub.2-2xFe.sub.2-xM.sub.xO.sub.4 (x is from 0 to 1) wherein M=P, V, Nb and/or Ta; Rb.sub.2-2xGa.sub.2-xM.sub.xO.sub.4 (x is from 0 to 1) wherein M=P, V, Nb and/or Ta; Rb.sub.2-2xAl.sub.2-xM.sub.xO.sub.4 wherein M=P, V, Nb and/or Ta; and Rb (x is from 0 to less than 1) wherein M=Si, Ti, and/or Ge.

(73) In some embodiments, the mixed ion-electron conductor material of the second electrode may be selected from alkali pyrophosphates, such as Rb.sub.4P.sub.2O.sub.7. The alkali pyrophosphate is optionally doped with one or more atoms selected from Ca, Sr, Ba, Pb, Y, La, and/or Nd, for example. Exemplary compounds for the ion-electron conductor include, but are not limited to, Rb.sub.4-2xM.sub.xP.sub.2O.sub.7 (x is from 0 to less than 2) wherein M=Ca, Sr, Ba, and/or Pb; and Rb.sub.3-3xM.sub.xPO.sub.4 (x is from 0 to less than 1) wherein M=Y, La, and/or Nd.

(74) In some embodiments, the second electrode contains an intercalable compound that is capable of being intercalated by at least one element (in ionic and/or neutral form) selected from the group consisting of Rb, Cs, Na, K, and Sr. The vapor-cell region vapor phase may include metal atoms that are intercalable in the intercalable compound of the second electrode.

(75) As used herein, an intercalable compound (or intercalatable compound) is a host material that is capable of forming an intercalation compound with guest atoms which comprise the atomic vapor in the vapor cell. Stated another way, the intercalable compound is intercalative for (capable of intercalating) at least some of the atoms in the atomic vapor. The guest atoms that are intercalated may be neutral atoms, ionic species, or a combination thereof. Typically, the guest atoms are intercalated as neutral atoms.

(76) In some embodiments, the host material actually contains the guest species, resulting in a material which may be referred to as an intercalation compound. It is noted that for the purposes of this patent application, any reference (e.g., in the drawings) to intercalable compound may be replaced by intercalation compound, and vice-versa, since an intercalable compound must be capable of intercalating a guest species but may or may not actually contain the intercalated guest species.

(77) Intercalation herein is not limited to the reversible inclusion or insertion of an atom, ion, or molecule sandwiched between layers present in a compound, which shall be referred to herein as layer intercalation. Intercalation also includes absorption of neutral atoms or ionic species into a bulk phase of the compound, whether that phase is amorphous or crystalline; adsorption of neutral atoms or ionic species onto an outer surface or an internal surface (e.g., a phase boundary) present in the compound; and reversible chemical bonding between the neutral atoms or ionic species, and the compound.

(78) Some embodiments of the invention utilize layer intercalation, in which a guest species such as K expands the van der Waals gap between sheets of a layered compound such as graphite. This layer expansion requires energy. Without being limited by theory, the energy may be supplied by electrical current to initiate charge transfer between the guest (K) and the host solid (C, graphite). In this example, potassium graphite compounds such as KC.sub.8 and KC.sub.24 may be formed. These compounds are reversible, so that when the electrical current is adjusted, the potassium graphite compounds may give up the intercalated atoms (K). Those previously intercalated atoms may be released into the vapor phase or into the ion-conducting layer, for example. Electrical energy may be supplied to cause a chemical potential change at the interface with the intercalable compound, which then causes layer expansion.

(79) In some embodiments, the intercalable compound is a carbonaceous material, such as a material selected from the group consisting of graphite, graphene, holey graphene, graphene platelets, carbon nanotubes, fullerenes, activated carbon, coke, pitch coke, petroleum coke, carbon black, amorphous carbon, glassy carbon, pyrolyzed carbon-containing molecules, pyrolyzed parylene, polyaromatic hydrocarbons, and combinations thereof.

(80) The carbonaceous material may be at least 50 wt % carbon, preferably at least 75 wt % carbon, more preferably at least 90 wt % carbon, most preferably at least 95 wt % carbon. In some embodiments, the carbonaceous material is essentially pure carbon, except for impurities. The carbonaceous material may include mesoporous carbon, microporous carbon, nanoporous carbon, or a combination thereof.

(81) The intercalable compound may be a form of predominately sp.sup.2 bonded carbon. Examples of sp.sup.2 bonded carbon include, but are not limited to, graphite, graphene, carbon nanotubes, carbon fibers, fullerenes (e.g. C.sub.60 or C.sub.70), pyrolyzed carbon-containing molecules or polymers (such as pyrolyzed parylene, e.g. parylene-N, parylene-C, or parylene-AF-4), and large polyaromatic hydrocarbons (e.g. pentacene, rubrene, hexabenzocoronene, or coronene). In the case of graphene (which is essentially a single layer of graphite), the graphene may be monolayer graphene or multiple layers of graphene. Graphene flakes (a few layers of graphene) may be utilized. Certain embodiments utilize monolayer holey graphene, multiple layers of holey graphene, or graphene platelets.

(82) In certain embodiments, the carbonaceous material comprises graphite. Graphite consists of planes of carbon sheets. Alkali atoms readily intercalate between these carbon sheets, leading to a high diffusivity for alkali atoms. Graphite electrodes enable fast alkali transport at low voltages and low power consumption per atom removed. Graphite transports not only atoms via intercalation, but also electricity due to the electron delocalization within the carbon layers. Valence electrons in the carbon are free to move, thereby conducting electricity through the graphite.

(83) The graphite may be natural graphite (e.g., mined graphite) or synthetic graphite produced from various techniques. For example, graphite may be obtained from chemical-vapor-deposited graphitic carbon, carbide-derived graphite, recycled graphite, waste from graphene manufacture, and so on. Crystalline flake graphite occurs as isolated, flat, plate-like particles with hexagonal edges if unbroken; when broken the edges can be irregular or angular. Amorphous graphite is very fine flake graphite. Lump graphite occurs in fissure veins or fractures and appears as massive platy intergrowths of fibrous or acicular crystalline aggregates. Highly oriented pyrolytic graphite is graphite with an angular spread between the graphite sheets of less than 1.

(84) The graphite may be crystalline, amorphous, or a combination thereof. The graphite crystallinity may range from about 10% to about 90%, for example. A mixture of crystalline and amorphous graphite may be beneficial for intercalation not only between crystal layers but also between crystalline and amorphous regions of the graphite. With too much crystallinity, the diffusivity becomes highly anisotropic. If highly crystalline (i.e. highly anisotropic) graphite is oriented with the low-diffusivity axis normal to the surface of the device (which is a typical orientation), reduced alkali flux, and thus reduced performance, would result.

(85) Functionalized carbon, such as graphite oxide or graphene oxide, may be employed in the intercalable compound of the second electrode.

(86) In other embodiments, the intercalable compound of the second electrode is a transition-metal oxide, a transition-metal dichalcogenide, or a combination thereof. The intercalable compound may also be a mixture of a carbonaceous material and a transition-metal oxide, or a mixture of a carbonaceous material and a transition-metal dichalcogenide, or a mixture of all of these materials. Specifically, the intercalable compound may be a metal dichalcogenide selected from MoS.sub.2, TaS.sub.2, TiTe.sub.2, or any other transition metal dioxide, disulfide, diselenide, or ditelluride.

(87) In some embodiments, the second electrode is fabricated from particles of an intercalable compound dispersed in a matrix. The matrix may be a polymer binder, such as polyvinylpyrrolidone, cellulose resin, fluoroelastomer, or polyacrylic. The polymer binder preferably has low outgassing potential and is compatible with ultra-high vacuum. Optionally, additives may be introduced into the matrix to increase the electrical conductivity of the second electrode. Such additives may be metals or small conductive carbon particles (e.g. Super-P Conductive Carbon Black).

(88) In some embodiments, the second electrode includes more than one layer, such as a Ti adhesion layer and a Pt layer, or a Cu layer and a graphite layer, for example.

(89) It is desirable that an electrical potential, when applied, does not vary considerably (e.g. <0.1 V) across the second electrode surface. Thus, the second electrode thickness is preferably selected based on the second-electrode material resistivity and the expected ionic current through the ion-conducting layer.

(90) The second electrode may be a uniform layer (e.g., FIG. 1A) or a non-uniform layer. The thickness of the second electrode may be less than 500 m or less than 100 m. In various embodiments, the thickness of the second electrode is about 1, 5, 10, 20, 30, 40, 50, 75, 100, 200, or 500 m.

(91) Each electrode is typically connected to an electrical lead fabricated from an electrically conductive material. A lead is an electrical connection consisting of a length of wire, metal pad, metal trace, or other electrically conductive structure. Leads are used to transfer power and may also provide physical support and potentially provide a heat sink. In some embodiments, a device is provided without such leads, which may be added at a later time, before use.

(92) A number of variations of the device are possible.

(93) The vapor cell may be situated inside a magnetic field. Coils of wire driven in an anti-Helmholtz configuration surrounding the vapor cell can be used to generate the magnetic fields required for the trap. Other magnetic-field sources (such as magnets or materials capable of generating magnetic flux) may be utilized to generate magnetic fields within the vapor-cell region. The magnetic-field source may be provided separately from the vapor cell, and these components may be assembled and disassembled from each other for various reasons.

(94) The vapor cell may be contained within an oven. The purpose of the oven may be to control the temperature of the vapor cell at a temperature above the ambient temperature, for example. In principle, the vapor cell may be contained within any sort of temperature-controlled system, for heating or cooling the vapor cell.

(95) A vapor-cell oven enables independent control over the alkali or alkaline earth partial pressure and an optional buffer gas partial pressure in the vapor cell. In some embodiments, the buffer gas partial pressure is controlled by the oven temperature and the alkali or alkaline earth partial pressure is controlled by the voltage and current applied across the solid electrolyte (ion-conducting layer). As conditions in the vapor cell change over time, the oven temperature and alkali or alkaline earth partial pressure can be adjusted to maintain a narrow, stable absorption peak. Because the alkali or alkaline earth atom concentration may be adjusted after the vapor cell is sealed, precision loading of alkali or alkaline earth metal is not necessary, thus making the sealing process significantly easier.

(96) The system may include one or more heaters to provide heat and thus temporarily increase the ionic conductivity of the ion-conducting layer. The heater is preferably a resistive heater, but may also be a thermoelectric heater, for example. The heater may be patterned directly on the ion-conducting layer, or on another part of the device. The heater may also be attached to a part of the device, or otherwise in thermal or electromagnetic communication (e.g., for induction heating) with the device.

(97) The device may be implemented at a wide variety of length scales. The length scale may be characterized by the cube root of the vapor chamber volume. This length scale may vary from 10 m to 1 nm, with 1 m to 10 mm being typical for macroscale atomic timing and navigation systems, and 10 mm to 10 microns being typical for chip-scale atomic timing and navigation systems.

(98) Chip-scale devices are preferably constructed using microfabrication techniques, including some or all of lithography, evaporation, shadow-masking, evaporation, sputtering, wafer bonding, die bonding, anodic bonding, glass frit bonding, metal-metal bonding, and etching.

(99) Multiple ionic conductors, each with their own electrodes, may be present in a single device. Multiple first electrodes may or may not be electrically connected through electrical leads or electrical traces. Likewise, multiple second electrodes may or may not be electrically connected through electrical leads or electrical traces.

(100) Multiple sets of first electrodes, ion-conducting layers, and second electrodes may generally be present.

(101) In some embodiments, two or more front electrodes are employed. In these or other embodiments, two or more back electrodes are employed. In any of these embodiments, or other embodiments, two or more ion conductors are employed.

(102) While at least one of these electrodes satisfies the requirements described above (i.e. as a MIEC material), the other electrodes present may be conventional electrodes such as a thin platinum grid. Dielectric materials may be employed to isolate and electrically insulate the electrodes from other parts of the system.

(103) One or more of the second electrodes may contain an alternate source of replacement ions for the ion-conducting layer. The alternate source of replacement ions may be a metal (e.g. silver), an ion-containing species (e.g. a salt), an intercalated compound (e.g. Rb intercalated into graphite), an intermetallic (e.g. gold and rubidium), or a solid or liquid elemental form of an alkali metal or an alkaline earth metal.

(104) In some embodiments, an intercalation compound (e.g. Rb intercalated into graphite) is a substantial portion of the second electrode. In the case of a solid or liquid alkali metal second electrode, the alkali metal may be capped with a non-reacting layer such as Pt to seal in the alkali metal and prevent corrosion and/or oxidation.

(105) When a potential is applied across a first electrode and a paired second electrode which contains an alternate source of replacement ions such that the first electrode is at a lower electrical potential than the second electrode, metal ions in the ion-conducting layer between the electrodes will migrate (i.e. conduct) towards the first electrode. They will be replaced by the replacement ions at the second electrode. This prevents the depletion of ions in the ion-conducting layer near the second electrode, thus preventing the charging of a pseudocapacitor which would otherwise require increasing electrical potential to transport more ions. However, this does contaminate the ion-conducting layer with the make-up replacement ions.

(106) In some embodiments, one or more of the second electrodes are configured to enable an electrochemical capacitor. It is preferable to configure such electrodes such that they contact as large of an area as possible of the ion-conducting layer, to increase the electrochemical pseudocapacitance. For instance, the ion-conducting layer may have a roughened, etched, trenched, crenulated, or ridged second surface to increase the contact area between itself and the second electrode(s).

(107) The vapor cell may also contain an atom chip for intra-system generation of magnetic fields for microtraps. The atom chip and the solid electrolyte need not be the same size. An atom chip may be disposed on a different vapor cell face from the solid electrolyte (ion-conducting layer). An atom chip may be fabricated on a base chip that is heterogeneously integrated with the solid electrolyte on the same vapor cell face. The atom chip may be closer to the vapor cell volume than the solid electrolyte, in which case the vapor atoms may pass around the edges of the atom chip or through one of more holes in the atom chip, for example. The solid electrolyte may be closer to the vapor cell than the atom chip, in which case the trapped population of cold atoms may be situated above the solid electrolyte.

(108) An atom chip may be fabricated directly on the solid electrolyte or on the first electrode. The atom chip traces that generate the magnetic fields for microtraps may be adjacent to the top electrode traces in this case. The atom chip traces that generate the magnetic fields for microtraps may be separated from the ion-conducting layer by a material which is both an electronic insulator and an ionic insulator (e.g., certain glass materials).

(109) One or more of the second (back) electrodes may be in contact with a reservoir volume. The reservoir volume may be hermetically sealed or may be in fluid communication with a larger system. The larger system, for example, could be part of a high-vacuum system containing pumps, pressure/vacuum gauges, atom dispensers, getters, getter pumps, getter sources, pill sources, etc. The reservoir volume may contain alkali metal or alkaline earth metal in a vapor phase, a solid phase, and/or a liquid phase. The reservoir overcomes the problem of a loss of metal atom vapor over time, replacing atoms that irreversibly adsorb onto or diffuse into the walls, for example.

(110) U.S. patent application Ser. No. 14/879,510 entitled VAPOR CELLS WITH ELECTRICAL CONTROL OF VAPOR PRESSURE, AND METHODS OF USING THE VAPOR CELLS filed Oct. 9, 2015 (commonly owned with the present patent application) is hereby incorporated by reference herein for its disclosure about reservoir regions that may be utilized in the vapor-cell system of this invention, in certain embodiments.

(111) When a reservoir region is present, the reservoir region also typically contains an alkali metal (e.g. Na, K, Cs, or Rb) and/or an alkaline earth metal (e.g., Be, Mg, Ca, or Sr). The reservoir region and the vapor-cell region preferably contain the same alkali or alkaline earth metal atoms, but that is not necessary.

(112) The reservoir region should be capable of vapor isolation from the vapor-cell region. By capable of vapor isolation as intended herein, it is meant that the vapor-cell region and the reservoir region can be configured such that vapor cannot freely flow (by convection or diffusion, referred to herein individually or collectively as vapor communication) between the vapor-cell region and the reservoir region. In some embodiments, a reservoir region is designed such that it is not ever in vapor communication with the vapor-cell regionunless there is some sort of leak or structural damage to the system. In certain embodiments, a closable valve is placed between the vapor-cell region and the reservoir region. In such embodiments, when the valve is optionally opened, the vapor-cell region and the reservoir region will temporarily be in vapor communication. However, the valve (if present) is normally closed, making the reservoir region in vapor isolation from the vapor-cell region.

(113) In some embodiments, the concentration of the alkali or alkaline earth metal in the reservoir region is greater than that of the vapor-cell region. In these or other embodiments, the volume of the reservoir region is smaller than that of the vapor-cell region. The total number of atoms of alkali or alkaline earth metal in the reservoir region may be larger or smaller than the total number of atoms of alkali or alkaline earth metal in the vapor-cell region. The alkali or alkaline earth metal atoms in the reservoir region are preferably in the vapor phase, but they may also be present in a liquid phase and/or a solid phase contained in the reservoir region. Optionally, the temperature and concentration of the vapor-cell alkali or alkaline earth metal are selected to ensure atoms of the vapor-cell alkali or alkaline earth metal are essentially in the vapor phase.

(114) Walls enclose the reservoir region, sealing it from the ambient environment. The walls may be fabricated from silicon, SiO.sub.2, fused silica, quartz, pyrex, metals, dielectrics, or a combination thereof, for example. Optionally, at least one of the walls includes a substantially transparent portion such that there is an optical path through the reservoir region.

(115) The reservoir region may be contained within an oven which can control the temperature of the vapor-cell reservoir. In some embodiments, the vapor-cell region is contained in an oven while the reservoir region is not, or is contained in a different thermal zone. In other embodiments, the reservoir region is contained in an oven while the vapor-cell region is not.

(116) In some embodiments, a second solid electrolyte is connected between either the vapor cell and the ambient or the reservoir and the ambient. There are two electrodes associated with this second solid electrolyte, one on each side. This second solid electrolyte could be used to load alkali or alkaline earth metal into the vapor-cell region or into the reservoir region. The alkali or alkaline earth loading operation may be done at the beginning of the life of the vapor-cell system. The alkali or alkaline earth loading operation may be repeated periodically through the life of the vapor-cell system. This loading operation is easier than loading a precise amount of alkali or alkaline earth vapor into an unsealed vapor cell and then sealing the vapor cell. An impermeable (or reduced permeability) layer may be placed over the solid electrolyte after loading to eliminate or reduce the diffusion of alkali or alkaline earth vapor out of the vapor-cell region and/or out of the reservoir region.

(117) The system may be configured to allow a secondary optical path through the reservoir region. Multiple laser beams may be employed, or the beam of a single laser may be split to interrogate both the primary and secondary optical paths. The difference in absorption between the two paths may be used to sense the difference in alkali or alkaline earth vapor pressure between the two chambers. If the alkali or alkaline earth in the reservoir is in a vapor-liquid or solid-vapor equilibrium, then the vapor pressure in the reservoir is known if the temperature of the reservoir is known. Thus, the vapor pressure of the alkali or alkaline earth in the vapor cell may be determined by knowing the difference in absorption between the two optical paths and the temperature of the reservoir.

(118) In some embodiments, the reservoir alkali or alkaline earth metal is present at a higher molar concentration in the reservoir region than the molar concentration of the vapor-cell alkali or alkaline earth metal in the vapor-cell region. The volume of the reservoir region is typically (but not necessarily) less than the volume of the vapor-cell region.

(119) In some embodiments, the system further comprises an additional solid electrolyte disposed in ionic communication between the vapor-cell region and an external source of alkali or alkaline earth metal, for initial or periodic loading of the vapor-cell region with the vapor-cell alkali or alkaline earth metal. In these or other embodiments, the system may include another solid electrolyte disposed in ionic communication between the reservoir region and an external source of alkali or alkaline earth metal, for initial or periodic loading of the reservoir region with the reservoir alkali or alkaline earth metal. The polarity of the voltage may be selected to control direction of alkali or alkaline earth atom flux, either from the reservoir region into the vapor-cell region, or from the vapor-cell region into the reservoir region. The amplitude of the voltage may be selected to control magnitude of alkali or alkaline earth atom flux.

(120) The system may include a membrane which deflects as the pressure inside the vapor cell changes. The deflection could be read out with an electrical signal (e.g. piezoelectric, capacitive, differential capacitive, etc.). The membrane could deflect as the pressure between the vapor cell and a reference cell changes. The reference cell may contain vacuum or may contain a substance in vapor-solid or vapor-liquid equilibrium such that the pressure inside the reference cell would be known by knowing the temperature of the reference cell.

(121) Reference is now made to the accompanying drawings, which should not be construed as limiting the invention in any way, but will serve to illustrate various embodiments. Note that with respect to all drawings, the second electrode may be a mixed ion-electron conductor, an intercalation-compound layer, a conventional metal electrode, another type of electrode, or a combination thereof.

(122) FIG. 1A is a schematic of an exemplary vapor cell, in some embodiments. In FIG. 1A, a single-layer mixed ion-electron conductor first (front) electrode is disposed in contact with the vapor-cell region. A single-layer mixed ion-electron conductor second (back) electrode is electrically isolated from the first electrode. An ion-conducting layer is interposed between the first electrode and the second electrode. The second electrode is in contact with an optional reservoir region containing metal atoms. FIG. 1A shows laser beams traversing three optical paths in the vapor cell and trapping a population of cold atoms. In some embodiments, the three optical paths are orthogonal to each other. FIG. 1A is a two-dimensional flattened projection of three orthogonal laser paths in three dimensions. An optional magnetic field source and resulting magnetic field lines, which also play a role in the trapping of atoms, are not depicted in this sketch.

(123) FIG. 1B is identical to FIG. 1A, except that the laser beams are not shown. It shall be understood that laser beams may or may not be present in any vapor cell described in this specification. That is, a source of laser beams may be present but not operating, in which case no laser beams will enter or be present within the vapor-cell region. Or a vapor cell may be provided without a source of laser beams, which source may be added at a later time, prior to operation of the vapor-cell system. In any event, the laser beams can be omitted from the drawings for clarity, it being understood that laser beams may be present. The remaining drawings (FIGS. 2-13) do not explicitly depict laser beams or optical paths, it being again understood that that laser beams may or may not be actually present, analogous to FIGS. 1A/1B. Likewise, magnetic field sources (external to the device) and magnetic field lines (within the device) are not depicted in the drawings, to aid in the depiction of device features and because the magnetic field sources and lines may or may not be actually present.

(124) FIG. 2 is a schematic of an exemplary vapor cell, in some embodiments. In FIG. 2, a dual-layer first (front) electrode includes a mixed ion-electron conductor layer and a porous electrically conductive layer. In addition, a dual-layer second (back) electrode includes a mixed ion-electron conductor layer and a porous electrically conductive layer. The porous electrically conductive layers preferably have electrical resistivity less than 10.sup.3 .Math.cm, more preferably less than 10.sup.4 .Math.cm, measured at 25 C. The porous electrically conductive layers may be thin (e.g., less than 200 nm) Pt meshes, for example. This may allow the desirable property that an electrical potential, when applied, does not vary considerably (e.g., <0.1 V) across the electrode surface. An ion-conducting layer is interposed between the first electrode and the second electrode. The second electrode is in contact with an optional reservoir region containing metal atoms.

(125) FIG. 3 is a schematic of an exemplary vapor cell, in some embodiments. In FIG. 3, there are two pairs of electrodes, in region A and in region B. Regions A and B are ionically connected via a common solid electrolyte ion-conductor. Region A is configured for reducing the vapor pressure of the vapor cell, by including a mixed ion-electron conductor layer on the side facing the vapor-cell region. Region B is configured for increasing the vapor pressure of the vapor cell, by including a mixed ion-electron conductor layer on the opposite side that faces the reservoir region. An ion-conducting layer is interposed between the first electrode and the second electrode. The second electrode is in contact with a reservoir region containing metal atoms.

(126) FIG. 4 is a schematic of an exemplary vapor cell, in some embodiments. A dual-layer first (front) electrode includes a mixed ion-electron conductor layer and a porous electrically conductive layer. In FIG. 4, there is no vapor region in the reservoir. Rather, the reservoir is combined with the second electrode and includes a thick intercalable-compound layer (e.g., graphite layer). An ion-conducting layer is interposed between the first electrode and the second electrode (which also functions as a solid reservoir).

(127) FIG. 5 is a schematic of an exemplary vapor cell, in some embodiments. A dual-layer first (front) electrode includes a mixed ion-electron conductor layer and a porous electrically conductive layer. In FIG. 5, there is no vapor region in the reservoir. Rather, the reservoir is combined with the second electrode and includes a thick intercalable-compound layer (e.g., graphite layer). An ion-conducting layer is interposed between the first electrode and the second electrode (which also functions as a solid reservoir). Additionally, in this variation, there are two pairs of electrodes (region A and region B). Region A is configured for reducing the vapor pressure of the vapor cell, by including a mixed ion-electron conductor layer on the side facing the vapor-cell region. Region B is configured for increasing the vapor pressure of the vapor cell, by including an intercalation compound layer on the opposite side that also forms a solid reservoir region.

(128) FIG. 6 is a plan-view schematic of a dual-layer electrode (including a mixed ion-electron conductor layer and a porous electrically conductive layer) disposed on an ion-conducting layer, in some embodiments.

(129) FIG. 7 is a plan-view schematic of a chip-scale variation of the invention, in some embodiments utilizing a dual-layer electrode including a mixed ion-electron conductor layer and a porous electrically conductive layer.

(130) FIG. 8 is a side-view schematic of a chip-scale variation of invention, in some embodiments utilizing a dual-layer first electrode including a mixed ion-electron conductor layer and a porous electrically conductive layer, and an intercalation-compound second electrode.

(131) FIG. 9 is a schematic of the invention, in some embodiments, integrated with an atom chip at the package level. In FIG. 8, a dual-layer first (front) electrode includes a mixed ion-electron conductor layer and a porous electrically conductive layer. A dual-layer second (back) electrode includes an intercalation-compound layer and a porous electrically conductive layer.

(132) FIG. 10 is a schematic of the invention, in some embodiments, with an atom chip heterogeneously integrated with the solid electrolyte ion-conductor.

(133) FIG. 11 is a schematic of the invention, in some embodiments, with an atom chip fully integrated with one of solid electrolyte ion conductor. In this case, the atom chip electrical traces are patterned with the ion-conducting membrane as a substrate.

(134) FIG. 12 is a plan-view schematic of electrodes and atom chip wires on an ion conductor in some embodiments of this invention, with an atom chip fully integrated with the ion conductor.

(135) FIG. 13 is an exemplary schematic of a method (process flowchart) of the invention, according to some embodiments.

(136) Some variations of the invention provide methods for operating a device described herein. Some methods include the following steps or configurations.

(137) In some embodiments, a voltage is applied between the first and second electrodes to reduce the atom vapor density in the vapor-cell region (e.g., evacuate some or all of the alkali atoms from the vapor cell). The voltage is applied such the second electrode has a lower electrical potential than the first electrode. This causes mobile ions within the solid electrolyte to conduct towards the second electrode and mobile ions within the first electrode to conduct towards and into the solid electrolyte. At the interface between the mixed ion-electron conductor and the vapor chamber volume, adsorbed alkali atoms are ionized, electrons conduct through the first electrode, and ions conduct through the first electrode. As atoms from the vapor chamber volume adsorb onto the mixed ion-electron conductor, those atoms are continuously transported into the first electrode, thus reducing the number of atoms in the vapor phase in the vapor-cell region.

(138) If the second electrode contains an intercalable compound, ions from the solid electrolyte will be neutralized by electrons supplied via the second electrode and the neutral atoms will intercalate into the second electrode material. If there is a reservoir with an atom vapor, ions from the solid electrolyte will be neutralized by electrons supplied via the second electrode, and neutral atoms will desorb from the surface of the ion-conducting layer into the alkali reservoir.

(139) Some embodiments include one or more of the following additional steps or configurations.

(140) A population of cold atoms (e.g., 10.sup.5 to 10.sup.9 atoms) at a temperature of, for example, about 1 K to 1000 K, may be prepared within the vapor-cell region prior to applying a voltage between the first and second electrodes, to reduce the atom vapor density in the vapor-cell region. This population may be formed with a magneto-optical trap.

(141) A voltage may be applied between the first and second electrodes to increase the atom vapor density in the vapor-cell region prior to preparing a population of cold atoms within the vapor-cell region. The voltage is applied such the second electrode has a higher electrical potential than the first electrode. This causes mobile ions within the solid electrolyte to conduct towards and into the first electrode. Additionally, ions will be conducted in the first electrode towards the interface between the first electrode and the vapor chamber volume. Ions from the first electrode will be neutralized by electrons supplied via the first electrode at the interface between the first electrode and the vapor chamber volume, forming neutral atoms. The neutral atoms will then desorb from the surface of the first electrode into the vapor-cell region, thus increasing the atomic density in the vapor-cell region.

(142) If there is a solid source of replacement ions, the replacement ions will enter the ion-conducting layer near the second electrode and prevent the formation of an ion-depletion region. If an ion-blocking electrode is present, then within the solid electrolyte near the second electrode a region partially or fully depleted in mobile ions will form. Immobile ions (e.g. AlO.sup. or O.sup.2) will remain. These immobile ions will form a pseudocapacitor balanced by the charge on the second electrode. These charges are physically separated. Metal ion flow will reduce and may eventually stop as more and more of the applied voltage drops across the pseudocapacitor region to maintain the charge separation.

(143) If there is a reservoir with atom vapor and the second electrode does not contain an intercalable material, then metal atoms will adsorb on the ion-conducting layer and/or the second electrode, ionize, and then the metal ions will enter the ion-conducting layer and replace the lost ions. If the second electrode contains an intercalable compound, atoms will diffuse down a concentration gradient in the second electrode away from the interface between the second electrode and the reservoir region, and towards the ion-conducting layer. Atoms will ionize at the interface of the second electrode and ion-conducting layer. Electrons will conduct through the electrode, and ions will conduct through the ion-conducting layer. As atoms diffuse away from the interface between the second electrode and the reservoir region, the intercalable compound will getter additional atoms from the vapor phase.

(144) After reducing the vapor pressure as described above, the trap on the population of cold atoms may be released and a measurement of frequency or position may be made. After the measurement, a population of cold atoms may be re-trapped, released, and a new measurement may be made. This step may be repeated multiple times. The entire cycle of steps could be repeated multiple times (e.g., see FIG. 13).

(145) One or more walls of the vapor chamber volume are substantially transparent at relevant wavelengths such that there is an optical path through the vapor cell volume. It is preferable that there are three orthogonal optical paths to facilitate the formation of a magneto-optical trap (MOT) and for atomic cloud imaging.

(146) Some embodiments provide a magneto-optical trap apparatus, the apparatus comprising:

(147) a vapor-cell region configured to allow three (preferably orthogonal) vapor-cell optical paths within a vapor-cell vapor phase in the vapor-cell region;

(148) a first electrode disposed in contact with the vapor-cell region, wherein the first electrode contains a first mixed ion-electron conductor compound;

(149) a second electrode that is electrically isolated from the first electrode; and

(150) an ion-conducting layer interposed between the first electrode and the second electrode, wherein the ion-conducting layer is in ionic communication with the second electrode, and wherein the ion-conducting layer is ionically conductive for at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+;

(151) optionally (e.g., for purposes of operation or for providing an integrated system) a source of laser beams configured to provide the three orthogonal vapor-cell optical paths through the vapor-cell gas phase, to trap a population of cold atoms; and

(152) optionally (e.g., for purposes of operation or for providing an integrated system) a magnetic-field source configured to generate magnetic fields within the vapor-cell region.

(153) The vapor-cell optical paths do not need to be orthogonal when entering the vapor cell. For example, there could be mirrors inside the vapor cell that make them orthogonal only inside the vapor cell. There could be one optical path entering the cell, which optical path is split within the vapor cell. In some embodiments, within the vapor cell, along three different orthogonal axes based on the location of trapped atoms, two optical paths (one in each direction) are located on each of the three axes.

(154) Some embodiments provide an atomic-cloud imaging apparatus, the apparatus comprising:

(155) a vapor-cell region configured to allow one or more (preferably orthogonal when more than one) vapor-cell optical paths within a vapor-cell vapor phase in the vapor-cell region;

(156) a first electrode disposed in contact with the vapor-cell region, wherein the first electrode contains a first mixed ion-electron conductor compound;

(157) a second electrode that is electrically isolated from the first electrode; and

(158) an ion-conducting layer interposed between the first electrode and the second electrode, wherein the ion-conducting layer is in ionic communication with the second electrode, and wherein the ion-conducting layer is ionically conductive for at least one ionic species selected from the group consisting of Rb.sup.+, Cs.sup.+, Na.sup.+, K.sup.+, and Sr.sup.2+;

(159) optionally (e.g., for purposes of operation or for providing an integrated system) a source of laser beams configured to provide the three orthogonal vapor-cell optical paths through the vapor-cell gas phase, to image a population of cold atoms; and

(160) optionally (e.g., for purposes of operation or for providing an integrated system) a magnetic-field source configured to generate magnetic fields within the vapor-cell region.

(161) In this detailed description, reference has been made to multiple embodiments and to the accompanying drawings in which are shown by way of illustration specific exemplary embodiments of the invention. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that modifications to the various disclosed embodiments may be made by a skilled artisan.

(162) Where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain steps may be performed concurrently in a parallel process when possible, as well as performed sequentially.

(163) All publications, patents, and patent applications cited in this specification are herein incorporated by reference in their entirety as if each publication, patent, or patent application were specifically and individually put forth herein.

(164) The embodiments, variations, and figures described above should provide an indication of the utility and versatility of the present invention. Other embodiments that do not provide all of the features and advantages set forth herein may also be utilized, without departing from the spirit and scope of the present invention. Such modifications and variations are considered to be within the scope of the invention defined by the claims.