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EPJ Quantum Technology

A low cost, short range quantum key distribution system

David Lowndes, Stefan Frick, Andy Hart, John Rarity

Published May 26, 2021• 27 citations
Publisher

Abstract

Abstract We present a miniaturized quantum key distribution system, designed to augment the more mature quantum key distribution systems currently commercially available. Our device is designed for the consumer market, and so size, weight and power are more important than raw performance. To achieve our form factor, the transmitter is handheld and the receiver is a larger fixed terminal. We envisage users would bring their transmitters to centrally located receivers and exchange keys which they could use at a later point. Transmitting qubits at 80 MHz, the peak key rate is in excess of 20 kbps. The transmitter device fits within an envelope of <150 ml, weighs 65 g and consumes 3.15 W of power.

DOI
10.1140/epjqt/s40507-021-00101-2

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Abstract We present a miniaturized quantum key distribution system, designed to augment the more mature quantum key distribution systems currently commercially available. Our device is designed for the consumer market, and so size, weight and power are more important than raw performance. To achieve our form factor, the transmitter is handheld and the receiver is a larger fixed terminal. We envisage users would bring their transmitters to centrally located receivers and exchange keys which they could use at a later point. Transmitting qubits at 80 MHz, the peak key rate is in excess of 20 kbps. The transmitter device fits within an envelope of <150 ml, weighs 65 g and consumes 3.15 W of power.
Mobile devices have become an inseparable part of our everyday life. They are used to transmit an ever-increasing amount of sensitive health, financial and personal information. This exposes us to the growing scale and sophistication of cyber-attacks. Quantum Key Distribution (QKD) can provide unconditional and future-proof data security but implementing it for handheld mobile devices comes with specific challenges. To establish security, secret keys of sufficient length need to be transmitted during the time of a handheld transaction (~1s) despite device misalignment, ambient light and user's inevitable hand movements. Transmitters and receivers should ideally be compact and low-cost, while avoiding security loopholes. Here we demonstrate the first QKD transmission from a handheld transmitter with a key-rate large enough to overcome finite key effects. Using dynamic beam-steering, reference-frame-independent encoding and fast indistinguishable pulse generation, we obtain a secret key rate above 30kb/s over a distance of 0.5m under ambient light conditions.
We present a Quantum Key Distribution system comprising a hand held transmitter device (Alice) and a fixed terminal (Bob). The devices are highly asymmetrical with as much functionality as possible placed into the Bob terminal (a 4u 19in. rack) which is much less restricted on its size. The small size (80x50x10mm) and relatively low complexity will allow the hand held Alice to be cheaply mass produced and therefore widely available. A potential use for this technology would be as a method to allow the general public to benefit from a wider metropolitan or national QKD network by establishing key with trusted network nodes. The Alice device optics comprise 4 pulsed 300um LEDs behind polarizers to produce the photon states for the BB84 protocol. Light from the LEDs is combined and spatially filtered using a single mode fibre, the output of which is collimated by a lens at the optical output of the device. The device is currently controlled via USB by a PC or mobile phone. The Bob terminal is split into two modules; broadly categorized as “optical” and “processing”. The optical module contains beam splitters for state discrimination and photon detection. The processing module contains a PC, wireless router, time-tagging electronics and power supply. The modular approach allows for a flexible platform for different QKD experiments, for example change of wavelength or protocol would involve switching out only the optical module. This work forms part of the Quantum Communications hub and was carried out with EPSRC funding (Quantum Communications Hub, grant no. EP/M013472/1).
Quantum key distribution is a well-established approach for sharing a classical key between two parties. In most cases, the parties are at fixed locations and use an optical fiber or free-space channel with fixed telescopes. To enable flexible and mobile quantum key distribution applications, we are developing a drone-based system. Here, the entire quantum transmitter and receiver system must have low size, weight, and power so that it can fly on medium-scale drones (Group 2, 21-55 lb gross takeoff weight). We will describe these key technologies and our current progress on achieving secure key exchange between drones.
We present a miniaturised free-space quantum key distribution (QKD) system which allows key exchange between a handheld transmitter and a fixed terminal. The QKD system requires to be optically aligned emphasising the need of a beamsteering unit for later applications. To maintain within the size, weight and power restrictions, the active beamsteering hardware is exclusively located inside the receiver. Our target is consumer use so we present rigorous characterisation against a range of background light levels to show anticipated performance outside of a laboratory environment. Experimental results show a reduction in the raw count rate commensurate with the transmission of the added components (74.5%) and a small degradation of the error rate (0.5 percentage points) due to the worse signal-to-noise ratio. These combine to a 50% reduction in estimated secret key rate of the system with the additional components for beam steering.
A Quantum Key Distribution system has been demonstrated with a focus on applicability of the technology to a consumer use model.The optical devices were split into a large, expensive "Quantum ATM" (the Bob terminal) and a small, cheap handheld section (the Alice device).Work was initially done to integrate the devices into a realistic demonstration system which was exhibited at several international conferences.Following this success, the devices constituent parts were isolated and improved upon.Work on the Alice device focused upon proposing a new scheme for light collimation and then investigating a method to enact this.In the Bob device the progress was directed towards a more effective single photon detection system utilizing active quenching.An asymptotic secure key rate of 20kb/s was obtained at a bit error rate (BER) of 4% corresponding to a daylight operation scenario.A docking scheme was enacted to simplify the alignment of the optical channel which was shown to be repeatable over at least 50 cycles.The system was also shown to be stable over an extended period of time.