Waveguide superconducting single-photon detectors for integrated quantum photonic circuits

The monolithic integration of single-photon sources, passive optical circuits, and single-photon detectors enables complex and scalable quantum photonic integrated circuits, for application in linear-optics quantum computing and quantum communications. Here, we demonstrate a key component of such a circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (similar to 20%) at telecom wavelengths, high timing accuracy (similar to 60 ps), and response time in the ns range and are fully compatible with the integration of single-photon sources, passive networks, and modulators. (C) 2011 American Institute of Physics. [doi:10.1063/1.3657518]

Optical characterisation of single quantum dots emitting at 1300nm

Carl Zinoni

This thesis deals with the optical characterization of single quantum dot devices emitting at 1300nm. Thanks to the development and optimization of the growth technique we were able to achieve at the same time emission at 1300nm and ultra low QD densities. Our single QD devices present clear and reproducible spectral signatures in which we can identify exciton, biexciton and charged exciton transitions. Quasi-resonant excitation at 70K demonstrates background free single exciton transitions, which is very promising for the realization of a single photon device operating at temperatures in easy reach of thermoelectric coolers. A time-correlated single photon counting setup was built and used to measure the radiative lifetimes of single exciton transitions. These measurements also present new evidence on a background emission superposed to the narrow spectral transitions. Demonstration of single photon emission at these wavelengths required building a setup to measure the correlations between fiber-coupled single photons in a 300ps time window, emitted from a nano-device in free space at cryogenic temperatures, and with the capability of maintaining the optical alignment on a micrometer scale for several hours. With such a setup we have demonstrated that our QDs can generate single photon states at 1300nm. We used this single photon source to characterize novel detectors based on superconducting nanowires and measured for the first time the intensity correlation function at 1300nm on single photons from a QD. These detectors show at least 2 orders of magnitude improvement on the signal to noise ratio as compared to InGaAs APDs; this is very important since, for a QKD system, the detector noise, amongst others, determines the maximum distance over which a secure key can be exchanged. It should be noted that, due to the di±culties in these measurements, to date there has been only one other clear demonstration of single photon emission at 1300nm.

EPFL2007

Superconducting nanowire photon-number-resolving detector at telecommunication wavelengths

Alessandro Gaggero, Konstantinos Lagoudakis, Francis Lévy, Francesco Marsili

Optical-to-electrical conversion, which is the basis of the operation of optical detectors, can be linear or nonlinear. When high sensitivities are needed, single-photon detectors are used, which operate in a strongly nonlinear mode, their response being independent of the number of detected photons. However, photon-number-resolving detectors are needed, particularly in quantum optics, where n-photon states are routinely produced. In quantum communication and quantum information processing, the photon-numberre-solving functionality is key to many protocols, such as the implementation of quantum repeaters(1) and linear- optics quantum computing(2). A linear detector with single-photon sensitivity can also be used for measuring a temporal waveform at extremely low light levels, such as in long-distance optical communications, fluorescence spectroscopy and optical time-domain reflectometry. We demonstrate here a photon-number-resolving detector based on parallel superconducting nanowires and capable of counting up to four photons at telecommunication wavelengths, with an ultralow dark count rate and high counting frequency.

Nature Publishing Group2008

Optical characterisation of single quantum dots emitting at 1300nm

Carl Zinoni

EPFL2007