We study a class of receiver-device-independent quantum key distribution protocols based on a prepare-and-measure setup which aims to simplify their implementation. The security of the presented protocols relies on the assumption that the sender, Alice, prepares states that have limited inner-products. Hence, Alice’s device is partially characterized. There is no explicit bound on the Hilbert space dimension required. The receiver’s, Bob’s, device demands no characterization and can be represented as a black-box. The protocols are therefore immune to attacks on Bob’s device, such as blinding attacks. The users can generate a secret key while monitoring the correct functioning of their devices through observed statistics. We report a proof-of-principle demonstration, involving mostly off-the-shelf equipment, as well as a high-efficiency superconducting nanowire detector. A positive key rate is demonstrated over a 4.8 km low-loss optical fiber with finite-key analysis.
In recent years, many applications have been proposed that require detection of light signals in the near-infrared (NIR) range with single-photon sensitivity and time resolution below 100 ps; notably laser ranging, biomedical imaging, quantum key distribution (QKD) and quantum information and communication experiments. The current state of the art in terms of timing resolution in the NIR range is a jitter below 20 ps achieved by superconducting nanowire single-photon detector (SNSPD). A more practical and compact alternative that does not require cryogenic cooling is represented by InGaAs/InP single-photon avalanche diodes (SPADs). Indeed, gated-mode SPADs can achieve a timing resolution below 50 ps at relatively high excess biases (above 7 V). However, despite their good performance in terms of photon detection efficiency, dark count rate and timing resolution, standard InGaAs/InP SPADs are limited by their afterpulsing noise to gated-mode operation, thus precluding their use in many applications.
Negative-feedback avalanche diodes (NFADs) are a special structure of InGaAs/InP SPADs where a monolitically-integrated quenching resistor is used to reduce the afterpulsing noise contribution hence allowing free-running operation. Here, we present our recent results on the characterization of the timing response of different NFAD detectors for temperatures down to 143 K that demonstrate how NFADs can achieve timing jitter down to 50 ps in an extended range of operating conditions.
Superconducting nanowire single photon detectors (SNSPD) made from amorphous superconductors have showed great promise for achieving high fabrication yields, due to the highly uniform nature of the films. We present progress on the development of SNSPD based on amorphous MoSi with a critical temperature of around 5 K, which is ideal for detector operation at temperatures of 1 – 2.5 K, accessible with widely available cryogenic systems. First generation devices have achieved a saturated internal efficiency from visible to near-infrared wavelengths, which is the first requirement for high overall system efficiency. The broadband response has allowed us to make a robust study the energy-current relation in these devices, which defines the current required for a saturated internal detection efficiency for a given incident photon energy. Contrary to previous studies with other material systems, we find a nonlinear energy-current relation, which is an important insight into the detection mechanism in SNSPDs. The latest generation devices have been embedded into an micro-cavity structure in order to increase the system detection efficiency, which has increased to over 65% at 1550 nm. The efficiency is believed to be limited by fabrication imperfections and we present ongoing progress towards improving this characteristic as well as the yield of the devices. Efforts are also being made towards increasing the maximum operating temperature of the devices.
In recent years, many applications have been proposed that require detection of light signals in the near-infrared range with single-photon sensitivity and time resolution down to few hundreds of picoseconds. InGaAs/InP singlephoton avalanche diodes (SPADs) are a viable choice for these tasks thanks to their compactness and ease-of-use. Unfortunately, their performance is traditionally limited by high dark count rates (DCRs) and afterpulsing effects. However, a recent demonstration of negative feedback avalanche diodes (NFADs), operating in the free-running regime, achieved a DCR down to 1 cps at 10 % photon detection efficiency (PDE) at telecom wavelengths. Here we present our recent results on the characterization of NFAD detectors for temperatures down to approximately 150 K. A FPGA controlled test-bench facilitates the acquisition of all the parameters of interest like PDE, DCR, afterpulsing probability etc. We also demonstrate the performance of the detector in different applications: In particular, with low-temperature NFADs, we achieved high secret key rates with quantum key distribution over fiber links between 100-300 km. But low noise InGaAs/InP SPADs will certainly find applications in yet unexplored fields like photodynamic therapy, near infrared diffuse optical spectroscopy and many more. For example with a large area detector, we made time-resolved measurements of singlet-oxygen luminescence from a standard Rose Bengal dye in aqueous solution.
Single-photon detectors are the best option for applications where low noise measurements and/or high timing
resolution are required. At wavelengths between 900 nm and 1700 nm, however, low noise detectors have typically
been based on cryogenic superconducting technology, precluding their extended use in industrial or clinical
applications. Here we present a practical (i.e. compact, reliable and affordable) detector, based on a negative
feedback InGaAs/InP avalanche photodiode and exhibiting dark counts < 1 count-per-second at 10% efficiency, and
with efficiencies of up to 27%. We show how this detector enables novel applications such as singlet-oxygen
luminescence detection for Photo Dynamic Therapy (PDT) but can be an enabling technology also for a diverse set
of applications in both quantum communication (e.g. long-distance quantum key distribution) and biomedical
imaging.
Free-running single photon detectors at telecom wavelengths are attractive for many tasks in quantum optics. However, until recently, the convenient and compact InGaAs/InP avalanche photodiodes did not operate with satisfactory performance in this regime due to high dark count rates and afterpulsing effects. Recent development of negative feedback avalanche diodes (NFADs) enabled very fast passive quenching of the avalanche current, effectively reducing the afterpulse probability and subsequently allowing free-running operation. Here, we present analysis of NFAD operation at low temperatures, down to 163 K, which reveals a significant reduction of the dark count rate. We succeeded in developing a compact single photon detection system with a dark count rate of ~1 cps at 10% detection efficiency. To ensure that the NFAD is in a well-defined initial condition during the characterization of the detection efficiency and afterpulsing, we use a recently developed FPGA based test procedure suitable for free-running detectors. To demonstrate the performance of the detector in a real-world application we integrate it into a 1.25 GHz clocked quantum key distribution system. An optimization of the detector temperature allowed secret key distribution in the presence of more than 30 dB of loss in the quantum channel.
Hugo Zbinden, Nino Walenta, Olivier Guinnard, Raphael Houlmann, Charles Lim Ci Wen, Boris Korzh, Tommaso Lunghi, Nicolas Gisin, Andreas Burg, Jeremy Constantin, Matthieu Legré, Patrick Trinkler, Dario Caselunghe, Natalia Kulesza, Gregory Trolliet, Fabien Vannel, Pascal Junod, Olivier Auberson, Yoan Graf, Gilles Curchod, Gilles Habegger, Etienne Messerli, Christopher Portmann, Luca Henzen, Christoph Keller, Christian Pendl, Michael Mühlberghuber, Christoph Roth, Norbert Felber, Frank Gürkaynak, Daniel Schöni, Beat Muheim
We present the results of a Swiss project dedicated to the development of high speed quantum key distribution and data encryption. The QKD engine features fully automated key exchange, hardware key distillation based on finite key security analysis, efficient authentication and wavelength division multiplexing of the quantum and the classical channel and one-time pas encryption. The encryption device allows authenticated symmetric key encryption (e.g AES) at rates of up to 100 Gb/s. A new quantum key can uploaded up to 1000 times second from the QKD engine.
We present gated silicon single photon detectors based on two commercially available avalanche photodiodes (APDs) and one customised APD from ID Quantique SA. This customised APD is used in a commercially available device called id110. A brief comparison of the two commercial APDs is presented. Then, the charge persistence effect of all of those detectors that occurs just after a strong illumination is shown and discussed.
We implement an InGaAs/InP single-photon avalanche diode (SPAD) for single-photon detection with the fastest
gating frequency reported so far, of 2.23GHz, which approaches the limit given by the bandwidth of the SPAD
- 2.5 GHz. We propose a useful way to characterize the afterpulsing distribution for rapid gating that allows for
easy comparison with conventional gating regimes. We compare the performance of this rapid gating scheme with
free-running detector and superconducting single-photon detector (SSPD) for the coherent one-way quantum key
distribution (QKD) protocol. The rapid gating system is well suited for both high-rate and long-distance QKD
applications, in which Mbps key rates can be achieved for distances less than 40km with 50 ns deadtime and the
maximum distance is limited to ~190km with 5 μs deadtime. These results illustrate that the afterpulsing is no
longer a limiting factor for QKD.
The distance in quantum communication is limited for direct transmission, but can be increased by the means
of entanglement swapping implemented in a quantum relay1 or quantum repeater configuration.2 Apart from
this, entanglement swapping is an intriguing phenomenon in quantum physics and deserves thus by itself to be
demonstrated in an experiment. Here we present an entanglement swapping experiment realized for the first
time with autonomous CW-sources.
Single photon detection at telecom wavelengths is of importance in many industrial applications ranging from quantum
cryptography, quantum optics, optical time domain reflectometry, non-invasive testing of VLSI circuits, eye-safe
LIDAR to laser ranging. In practical applications, the combination of an InGaAs/InP APD with an appropriate
electronic circuit still stands as the best solution in comparison with emerging technologies such as superconducting
single photon detectors, MCP-PMTs for the near IR or up-conversion technique.
An ASIC dedicated to the operation of InGaAs/InP APDs in both gated mode and free-running mode is presented. The
1.6mm2 chip is fabricated in a CMOS technology. It combines a gate generator, a voltage limiter, a fast comparator, a
precise timing circuit for the gate signal processing and an output stage. A pulse amplitude of up to +7V can be
achieved, which allows the operation of commercially available APDs at a single photon detection probability larger
than 25% at 1.55&mgr;m. The avalanche quenching process is extremely fast, thus reducing the afterpulsing effects. The
packaging of the diode in close proximity with the quenching circuit enables high speed gating at frequencies larger
than 10MHz. The reduced connection lengths combined with impedance adaptation technique provide excellent gate
quality, free of oscillations or bumps. The excess bias voltage is thus constant over the gate width leading to a stable
single photon detection probability and timing resolution. The CMOS integration guarantees long-term stability,
reliability and compactness.
We implement an OTDR with photon-counting modules at 1550nm based on sum frequency generation in a PPLN waveguide. The narrow temporal response of those detectors allows achieving a 2-points resolution of few centimetres.
Quantum Key Distribution (QKD) consists in the exchange of a secrete key between two distant
points [1]. Even if quantum key distribution systems exist and commercial systems are reaching
the market [2], there are still improvements to be made: simplify the construction of the system;
increase the secret key rate. To this end, we present a new protocol for QKD tailored to work with
weak coherent pulses and at high bit rates [3]. The advantages of this system are that the setup is
experimentally simple and it is tolerant to reduced interference visibility and to photon number
splitting attacks, thus resulting in a high efficiency in terms of distilled secret bits per qubit.
After having successfully tested the feasibility of the system [3], we are currently developing a fully integrated and automated prototype within the SECOQC project [4]. We present the latest results using the prototype. We also discuss the issue of the photon detection, which still remains the bottleneck for QKD.
Quantum key distribution (QKD) is stepping out of the lab. We present a commercial fibre-optic QKD-prototype based on faint laser pulses and the results of field tests. Faint laser, single photon and entangled-photon based systems are compared with respect to possible bit rates, detector noise and security and their possible implementation in a commercial apparatus.
In this paper we propose various applications of guided wave optics to quantum optics experiments. As quantum optics moves on to multiparticle and multiport configurations, guided wave optics, incorporating both integrated optics and fiber optics, could provide a realistic means of constructing experiments and devices.
We discuss three problems of practical quantum cryptography: continuous alignment, nose of the photon counters and eavesdropping. We present a new self-balanced interferometric setup using Faraday mirrors. This phase- coding setup needs no alignment of the interferometer nor polarization control, and therefore considerably facilitates the experiment. Moreover it features excellent fringe visibility. The importance of the detector noise is illustrated and means of reducing it are presented. Maximal distances and bit rates achievable with present day technologies are evaluated. Finally, practical eavesdropping strategies taking advantages of the optical fiber that could open a gate into the transmitter's receiver's offices are discussed.
A nondestructive technique that provides near-field measurements as well as refractive index profiles and geometry of waveguides in LiNbO3 within a few minutes is demonstrated. It is a modification of the refracted-near-field (RNF) method well known for optical fiber characterization. Spatial resolution below 1 μm is achieved. The index resolution is about 2 x 10-4, the reproducibility better than 7%. A new calibration method for RNF measurement is introduced.
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