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Optics Express

Handheld free space quantum key distribution with dynamic motion compensation

Hyunchae Chun, Iris Choi, Grahame E. Faulkner, Larry Clarke, Bryan Barber, Glenn George, Colin Capon, Antti Niskanen, Joachim Wabnig, Dominic C. O'Brien, David Bitauld

Published Mar 15, 2017• 66 citations
Publisher

Abstract

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.

DOI
10.1364/oe.25.006784

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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.
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.
Quantum key distribution (QKD) is moving from research laboratories towards applications. As computing becomes more mobile, cashless as well as cardless payment solutions are introduced. A possible route to increase the security of wireless communications is to incorporate QKD in a mobile device. Handheld devices present a particular challenge as the orientation and the phase of a qubit will depend on device motion. This problem is addressed by the reference frame independent (RFI) QKD scheme. The scheme tolerates an unknown phase between logical states that vary slowly compared to the rate of particle repetition. Here we experimentally demonstrate the feasibility of RFI QKD over a free-space link in a prepare and measure scheme using polarization encoding. We extend the security analysis of the RFI QKD scheme to be able to deal with uncalibrated devices and a finite number of measurements. Together these advances are an important step towards mass production of handheld QKD devices.
Mastering the generation, propagation and detection of electro-magnetic waves has enabled a technological breakthrough that has changed our entire society. World-wide communication through the telephone and the internet has become an integral part of our daily-life, which is expected to grow even further with the emergence of the internet of things. While secure communication was of concern mostly for governmental and financial institutions, digital security has now caught the attention of the general public. The weaknesses of cur- rent encryption protocols, such as the existence of back-doors or the predicted breakdown of popular algorithms such as RSA, reveal the need for alternative encryption schemes ensuring unconditional security on all types of devices. Quantum Key Distribution (QKD) has emerged as a powerful option to ensure a private communication between two users. Based on the laws of quantum mechanics, this class of protocols offers the possibility to detect the presence of a third party trying to intercept the key during its distribution, and even to quantify the amount of leaked information. While most research projects focus on long distance applications, little attention has been devoted to short distance schemes such as wireless payment, network access and authentication, which could highly benefit from QKD-enhanced security. This thesis focuses on the development of a miniature QKD sender add-on that could be embedded either in mobile devices or in existing optical communication platforms, thus allowing for a secure key exchange with a shared dedicated receiver over a free- space link. The proposed optics architecture (35 × 20 × 8 mm 3 ) is optimised for BB84-like protocols and uses an array of four Vertical-Cavity Surface-Emitting Lasers with highly similar properties to generate 40 ps long near-infrared faint coherent pulses at 100 MHz repetition rate. Under strong modulation, the polarisation of the pulses is not well defined and enables an external control of each diode’s emission by a wire-grid polariser. The four beams are spatially overlapped in a polarisation-insensitive femtosecond laser written waveguide array, and combined with a red beacon laser using an external beamsplitter to ensure a stable, synchronised optical link with the receiver. The complete module is compatible with current smartphone technology, allowing to run the classical post-processing over WLAN in the future. First tests with a free-space receiver indicate an average error ratio of 3.3 % and an asymptotic secure key rate of 54 kHz under static alignment. For the first time, a secure key exchange between a mobile platform held by a user and a receiver equipped with a dynamic alignment system could be demonstrated with an error ratio of 4.1 % and a secure key rate of 31 Hz. The further optimisation of the experimental parameters and the implementation of a decoy protocol will enhance the key generation rate as well as the general security of the system. The results of this thesis pave the way towards unprecedented security in wireless optical networks, as examplified for the communication between a mobile device and a dedicated receiver.
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.
Abstract Quantum key distribution (QKD) [1] is the first method of quantum information science that will find its way into our everyday life. It employs fundamental laws of quantum physics to ensure provably secure symmetric key generation between two parties. The key can then be used to encrypt and decrypt sensitive data with unconditional security. Here, we report on a free space QKD implementation using strongly attenuated laser pulses over a distance of 480 m. It is designed to work continuously without human interaction. Until now, it produces quantum keys unattended at night for more than 12 hours with a sifted key rate of more than 50 kbit/s and a quantum bit error rate between 3% and 5%.
The reference-frame-independent quantum key distribution (RFI QKD) protocol enables QKD systems to function effectively despite slowly varying reference frames, offering a distinct advantage in practical scenarios, particularly in mobile platforms. In this study, we successfully distribute secure key bits over a 250-km optical fiber distance by developing an RFI QKD system with a repetition rate of 150 MHz. Benefiting from high repetition rate, we achieve a finite-key secret key rate of 49.65 bit/s at a distance of 200 km, which is more than 3 times higher than state-of-the-art systems. Our work dramatically extends the transmission distance and enhances the secret key rate of RFI QKD, significantly promoting its practical application.