A quantum computing system that includes a quantum circuit device having at least one operating frequency; a first substrate having a first surface on which the quantum circuit device is disposed; a second substrate having a first surface that defines a recess of the second substrate, the first and second substrates being arranged such that the recess of the second substrate forms an enclosure that houses the quantum circuit device; and an electrically conducting layer that covers at least a portion of the recess of the second substrate.

A quantum computing apparatus, including a quantum circuit device; and an interposer including a connectorization layer including a plurality of terminals for connecting the quantum computing apparatus to a corresponding plurality of cables and a plurality of signal lines electrically coupled, via electrical contacts, to the plurality of terminals; and at least one intermediate layer between the quantum circuit device and the connectorization layer, the at least one intermediate layer comprising an integrated circuit layer, the at least one intermediate layer being electrically coupled to the signal lines of the interposer. The interposer is configured to supply the quantum circuit device, during operation of the quantum computing apparatus, at least control signals and readout signals to and from the plurality of cables.

A silicon-based quantum dot device (1) is disclosed. The device comprises a substrate (8) and a layer (7) of silicon or silicon-germanium supported on the substrate which is configured to provide at least one quantum dot (5.sub.1, 5.sub.2: FIG. 5). The layer of silicon or silicon-germanium has a thickness of no more than ten monolayers. The layer of silicon or silicon-germanium may have a thickness of no more than eight or five monolayers.

A Probabilistic Quantum Circuit with Fallback (PQFs) is composed as a series of circuit stages that are selected to implement a target unitary. A final stage is conditioned on unsuccessful results of all the preceding stages as indicated by measurement of one or more ancillary qubits. This final stage executes a fallback circuit that enforces deterministic execution of the target unitary at a relatively high cost (mitigated by very low probability of the fallback). Specific instances of general PQF synthesis method and are disclosed with reference to the specific Clifford+T, Clifford+V and Clifford+π/12 bases. The resulting circuits have expected cost in log.sub.b(1/ε(log(log(1/ε)))+const wherein b is specific to each basis. The three specific instances of the synthesis have polynomial compilation time guarantees.

Methods and devices are disclosed for implementing quantum information processing based on electron spins in semiconductor and transition metal compositions. The transition metal electron orbitals split under semiconductor crystal field. The electron ground states are used as qubits. The transitions between the ground states involve electron spin flip. The semiconductor and transition metal compositions may be further included in optical cavities to facilitate quantum information processing. Quantum logic operations may be performed using single color or two color coherent resonant optical excitations via an excited electron state.

Devices, methods and articles advantageously allow communications between qubits to provide an architecture for universal adiabatic quantum computation. The architecture includes a first coupled basis A.sub.1B.sub.1 and a second coupled basis A.sub.2B.sub.2 that does not commute with the first basis A.sub.1B.sub.1.

Devices, methods and articles advantageously allow communications between qubits to provide an architecture for universal adiabatic quantum computation. The architecture includes a first coupled basis A.sub.1B.sub.1 and a second coupled basis A.sub.2B.sub.2 that does not commute with the first basis A.sub.1B.sub.1.

A multiple-atom germanium quantum dot is provided that includes multiple dangling bonds on an otherwise H-terminated germanium surface, each dangling bonds having one of three ionization states of +1, 0 or −1 and corresponding respectively to 0, 1, or 2 electrons in a dangling bond state. The dangling bonds together in close proximity and having the dangling bond states energetically in the germanium band gap with selective control of the ionization state of one of the dangling bonds. A new class of electronics elements is provided through the inclusion of at least one input and at least one output to the multiple dangling bonds. Selective modification or creation of a dangling bond is also detailed.

In a general aspect, a tunable qubit device is identified that exhibits a frequency-dependent energy relaxation process in a quantum processor cell. The frequency-dependent energy relaxation process is produced by a material defect in the quantum processor cell. A first qubit frequency associated with a first relaxation time of the tunable qubit device is identified and a second qubit frequency associated with a second relaxation time of the tunable qubit device is identified. The second relaxation time is shorter than the first due to the frequency-dependent energy relaxation process produced by the material defect. The tunable qubit device is operated at the first qubit frequency while processing quantum information in the quantum processor cell. The tunable qubit device is tuned from the first qubit frequency to the second qubit frequency. A qubit state of the qubit device is reset by the frequency-dependent energy relaxation process produced by the material defect.

A multiple-atom silicon quantum dot is provided that includes multiple dangling bonds on an otherwise H-terminated silicon surface, each dangling bonds having one of three ionization states of +1, 0 or 1 and corresponding respectively to 0, 1, or 2 electrons in a dangling bond state. The dangling bonds together in close proximity and having the dangling bond states energetically in the silicon band gap with selective control of the ionization state of one of the dangling bonds. A new class of electronics elements is provided through the inclusion of at least one input and at least one output to the multiple dangling bonds. Selective modification or creation of a dangling bond is also detailed.