A high-speed multi-protocol quantum key distribution transmitter based on a dual-drive modulator

We propose a novel source based on a dual-drive modulator that is adaptable and allows Alice to choose between various practical quantum key distribution (QKD) protocols depending on what receiver she is communicating with. Experimental results show that the proposed transmitter is suitable for implementation of the Bennett and Brassard 1984 (BB84), coherent one-way (COW) and differential phase shift (DPS) protocols with stable and low quantum bit error rate. This could become a useful component in network QKD, where multi-protocol capability is highly desirable.Comment: 15 pages, 7 figure

Intrinsically stable light source at telecom wavelengths

We present a highly stable light source at telecom wavelengths, based on a short erbium doped fiber. The high stability arises from the high inversion of the Er3+ion population. This source is developed to work as a stable reference in radiometric applications and is useful in any application where high stability and/or a large bandwidth are necessary. The achieved long-term stability is 10 ppm

Practical fast gate rate InGaAs/InP single-photon avalanche photodiodes

We present a practical and easy-to-implement method for high-speed near infrared single-photon detection based on InGaAs/InP single-photon avalanche photodiodes (SPADs), combining aspects of both sine gating and self-differencing techniques. At a gating frequency of 921 MHz and temperature of -30 $^{\circ}$C we achieve: a detection efficiency of 9.3 %, a dark count probability of 2.8$\times10^{-6}$ ns$^{-1}$, while the afterpulse probability is 1.6$\times10^{-4}$ ns$^{-1}$, with a 10 ns "count-off time" setting. In principle, the maximum count rate of the SPAD can approach 100 MHz, which can significantly improve the performance for diverse applications.Comment: 3 pages and a few lines, 5 figures, 1 table. Accepted by Applied Physics Letter

Quantum random number generation on a mobile phone

Quantum random number generators (QRNGs) can significantly improve the security of cryptographic protocols, by ensuring that generated keys cannot be predicted. However, the cost, size, and power requirements of current QRNGs has prevented them from becoming widespread. In the meantime, the quality of the cameras integrated in mobile telephones has improved significantly, so that now they are sensitive to light at the few-photon level. We demonstrate how these can be used to generate random numbers of a quantum origin

Absolute calibration of fiber-coupled single-photon detector

We show a setup for characterising the efficiency of a single-photon-detector absolutely and with a precision better of 1%. Since the setup does not rely on calibrated devices and can be implemented with standard-optic components, it can be realised in any laboratory. Our approach is based on an Erbium-Doped-Fiber-Amplifier (EDFA) radiometer as a primary measurement standard for optical power, and on an ultra-stable source of spontaneous emission. As a proof of principle, we characterise the efficiency of an InGaAs/InP single-photon detector. We verified the correctness of the characterisation with independent measurements. In particular, the measurement of the optical power made with the EDFA radiometer has been compared to that of the Swiss Federal Office of Metrology using a transfer power meter. Our approach is suitable for frequent characterisations of high-efficient single-photon detectors.Comment: 14 pages, 4 figure

Creating high dimensional time-bin entanglement using mode-locked lasers

We present a new scheme to generate high dimensional entanglement between two photonic systems. The idea is based on parametric down conversion with a sequence of pump pulses generated by a mode-locked laser. We prove experimentally the feasibility of this scheme by performing a Franson-type Bell test using a 2-way interferometer with path-length difference equal to the distance between 2 pump pulses. With this experiment, we can demonstrate entanglement for a two-photon state of at least dimension D=11. Finally, we propose a feasible experiment to show a Fabry-Perot like effect for a high dimensional two-photon state.Comment: 5 pages, 5 figure

What are single photons good for?

In a long-held preconception, photons play a central role in present-day quantum technologies. But what are sources producing photons one by one good for precisely? Well, in opposition to what many suggest, we show that single-photon sources are not helpful for point to point quantum key distribution because faint laser pulses do the job comfortably. However, there is no doubt about the usefulness of sources producing single photons for future quantum technologies. In particular, we show how single-photon sources could become the seed of a revolution in the framework of quantum communication, making the security of quantum key distribution device independent or extending quantum communication over many hundreds of kilometers. Hopefully, these promising applications will provide a guideline for researchers to develop more and more efficient sources, producing narrowband, pure and indistinguishable photons at appropriate wavelengths.Comment: 6 pages, 5 figures, submitted to the special issue of the Journal of Modern Optics on the Single-Photon Workshop 201

Finite-key analysis on the 1-decoy state QKD protocol

It has been shown that in the asymptotic case of infinite-key length the 2-decoy state QKD protocol outperforms the 1-decoy state protocol. Here, we present a finite-key analysis of the 1-decoy method. Interestingly, we find that for practical block sizes of up to $10^8$ bits, the 1-decoy protocol achieves for almost all experimental settings higher secret key rates than the 2-decoy protocol. Since using only one decoy is also easier to implement, we conclude that it is the best choice for practical QKD.Comment: 6 pages, 7 figures, Pape

Afterpulsing studies of low noise InGaAs/InP single-photon negative feedback avalanche diodes

We characterize the temporal evolution of the afterpulse probability in a free-running negative feedback avalanche diode (NFAD) over an extended range, from $\sim$300 ns to $\sim$1 ms. This is possible thanks to an extremely low dark count rate on the order of 1 cps at 10% efficiency, achieved by operating the NFAD at a temperatures as low as 143 K. Experimental results in a large range of operating temperatures (223-143 K) are compared with a legacy afterpulsing model based on multiple trap families at discrete energy levels, which is found to be lacking in physical completeness. Subsequently, we expand on a recent proposal which considers a continuous spectrum of traps by introducing well defined edges to the spectrum, which are experimentally observed.Comment: 9 pages, 5 figure

Quantum Cloning for Absolute Radiometry

In the quantum regime information can be copied with only a finite fidelity. This fidelity gradually increases to 1 as the system becomes classical. In this article we show how this fact can be used to directly measure the amount of radiated power. We demonstrate how these principles could be used to build a practical primary standard