APPARATUS AND METHOD FOR QUANTUM ENHANCED PHYSICAL LAYER SECURITY

Abstract

A quantum key distribution (QKD) system comprising: an emitter (110) adapted to generate a QKD free-space signal, a transmitter station (220) adapted to receive the free-space signal from the emitter (110), and a remote QKD receiving station (250) supporting a QKD receiver (160) located at a different location than the transmitter station, wherein the transmitter station is adapted to receive said free space signal from the emitter and to forward said signal through a fiber link (400) to the QKD receiver (160) in said remote QKD receiving station (250).

Claims

1. A quantum key distribution (QKD) system comprising: an emitter (110) adapted to generate a QKD free-space signal, a transmitter station (220) adapted to receive the free-space signal from the emitter (110), and a remote QKD receiving station (250) supporting a QKD receiver (160) located at a different location than the transmitter station, wherein the transmitter station is adapted to receive said free space signal from the emitter and to forward said signal through a fiber link (400) to the QKD receiver (160) in said remote QKD receiving station (250).

2. The quantum key distribution (QKD) system of claim 1, wherein the emitter (110) is a high-altitude platform (HAP), preferably a satellite.

3. The quantum key distribution (QKD) system of claim 1, wherein the transmitter station (220) sends said free-space signal to the QKD receiver (160) without processing it.

4. The quantum key distribution (QKD) system of claim 1, wherein the transmitter station (220) is not a trusted node.

5. The quantum key distribution (QKD) system of claim 1, wherein transmitter station (220) is an optical ground station comprising a telescope (130) and a fiber coupling (140) for directing the free-space received optical signal into an optical fiber (400).

6. The quantum key distribution (QKD) system of claim 1, wherein the optical fiber (400) is a Single Mode Fiber (SMF) enabling long-distance distribution.

7. The quantum key distribution (QKD) system of claim 1, wherein the light is at a wavelength corresponding to a low-loss window in the fiber, around 1310 nm or around 1550 nm.

8. The quantum key distribution (QKD) system of claim 1, wherein the QKD receiving station (250) is at a distance ranging from a few hundred meters to several tens of kilometer from the transmitter station (220).

9. The quantum key distribution (QKD) system of claim 1, wherein the transmitter station (220) is located at a high altitude and/or non-urban location.

10. A quantum key distribution (QKD) method comprising the steps of: emitting a free-space signal from an emitter (110) to a transmitter station (220) adapted to receive said free-space signal from the emitter (110), directing said free-space received optical signal into an optical fiber, and sending the received signal through an optical fiber to a remote receiver supporting a QKD receiver (160) located at a different location than the transmitter station.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be described with reference to the drawings, in which the same reference numerals indicate the same feature. In particular,

[0032] FIG. 1 is a schematic representation of the principle of a Trusted Node;

[0033] FIG. 2 is a schematic representation of a conventional Free-space QKD system where the OGS is a trusted node; and

[0034] FIG. 3 is a schematic representation of a Free-space QKD system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The invention will be described, for better understanding, with reference to a specific embodiment. It will however be understood that the invention is not limited to the embodiment herein described but is rather defined by the claims and encompasses all embodiments which are within the scope of the claims.

[0036] FIG. 3 schematically illustrates a preferred embodiment of the invention which is a quantum key distribution (QKD) system 200 wherein an emitter, preferably a high-altitude platform 110, more preferably a satellite or the same, is linked to a transmitter station, preferably an optical ground station (OGS) 220 via a free-space link 300. In this embodiment, the OGS 220 is preferably located at an optimal location such as at high altitude and away from an urban center for maximizing the signal quality. The transmitter station 220 contains a telescope 130 and a fiber coupling 140 for directing the free-space received optical signal into an optical fiber 400 without processing it. As shown, the transmitter station 220 is connected to a remote QKD Receiving Station 250 supporting a QKD receiver 160 via a fiber link 400, which is directly connected to the QKD receiver 160 where the QKD receiver is preferably located far away, such as 30 km or more, from the transmitter station. In this regard, the fiber 400 has a predetermined length permitting avoiding the trusted node requirement for the transmitter station 220 and guarantees the security and the high quality of the quantum keys.

[0037] With this system 200, the light from the free-space channel 300 is directed to the fiber coupling 140 so as to be directly coupled, with the fiber coupling 140, without QKD process, into a low loss fiber 400 within the transmitter station 220 and then sent from the transmitter station 220 to the QKD receiver 160 through the fiber.

[0038] Typically, to enable long-distance distribution, the fiber 400 should be a Single Mode Fiber (SMF), and the light should be at a wavelength corresponding to a low-loss window in the fiber, typically the O-band (around 1310 nm) or the C-band (around 1550 nm).

[0039] Due to atmospheric disturbances, the wavefront of the light arriving at the transmitter station 220 is distorted. Distortions also evolve in time. Therefore, in order to couple it into a SMF, adaptive optics are preferred.

[0040] The light coupled into the SMF is then transported to the final QKD receiving station 250 hosting the QKD receiver 160, possibly several kilometers away, preferably ranging from a few hundred meters, corresponding to the transmitter station 220 being located for example on the top of a building, to several tens of kilometers, corresponding to the transmitter station being located away from a urban location.

[0041] The overall key distribution channel is therefore a hybrid channel, consisting of a free-space section 300, from the satellite 110 to the transmitter station 220, and an optical fiber-based section 400, which transports the light from the transmitter station 220 to the final QKD receiving station 250. Typically, the final receiving station 250 should be at the location of the end-user, who uses the keys for cryptographic purposes while the transmitter station 220 shall be located at optimal location in terms of signal quality, e.g. at high altitude and away from urban disturbance.

[0042] In this way, no key is generated at the transmitter station 220 but only at the QKD receiving section 250, after having passed through the whole hybrid channel.

[0043] As a consequence, the transmitter station 220 does not need to be a trusted node, while, at the meantime, the system is secure against attacks, since any eavesdropper trying to measure the data will perturb the quantum states and will be revealed by the QKD protocol.

[0044] Additionally, this implementation allows to select a better position for transmitter station 220, which can yield the following advantages:

[0045] 1. It increases the availability of the channel, by selecting a location with less cloud cover.

[0046] 2. It increases the key rate, by lowering the attenuation of the free-space channel (higher altitude and/or less polluted air)

[0047] 3. It lowers the bit error rate in the channel, by lowering the background noise due to stray light.

[0048] All three effects combine to increase the amount a secret key available per pass of the satellite/high-altitude platform, consequently enhancing the performances of the QKD.

[0049] While the embodiments have been described in conjunction with a number of embodiments, it is evident that many alternatives, modifications and variations would be or are apparent to those of ordinary skill in the applicable arts. Accordingly, this disclosure is intended to embrace all such alternatives, modifications, equivalents and variations that are within the scope of this disclosure. This for example particularly the case regarding the different apparatuses which can be used and the different types of protocol which are run.