High-detection efficiency and low-timing jitter with amorphous superconducting nanowire single-photon detectors

Recent progress in the development of superconducting nanowire single-photon detectors (SNSPDs) made of amorphous material has delivered excellent performances, and has had a great impact on a range of research fields. Despite showing the highest system detection efficiency (SDE) ever reported with SNSPDs, amorphous materials typically lead to lower critical currents, which impacts on their jitter performance. Combining a very low jitter and a high SDE remains a challenge. Here, we report on highly efficient superconducting nanowire single-photon detectors based on amorphous MoSi, combining system jitters as low as 26 ps and a SDE of 80% at 1550 nm. We also report detailed observations on the jitter behaviour, which hints at intrinsic limitations and leads to practical implications for SNSPD performance

Optically probing the detection mechanism in a molybdenum silicide superconducting nanowire single-photon detector

We experimentally investigate the detection mechanism in a meandered molybdenum silicide superconducting nanowire single-photon detector by characterising the detection probability as a function of bias current in the wavelength range of 750–2050 Onm. Contrary to some previous observations on niobium nitride or tungsten silicide detectors, we find that the energy-current relation is nonlinear in this range. Furthermore, thanks to the presence of a saturated detection efficiency over the whole range of wavelengths, we precisely quantify the shape of the curves. This allows a detailed study of their features, which are indicative of both Fano fluctuations and position-dependent effects

Heralded distribution of single-photon path entanglement

We report the experimental realization of heralded distribution of single-photon path entanglement at telecommunication wavelengths in a repeater-like architecture. The entanglement is established upon detection of a single photon, originating from one of two spontaneous parametric down conversion photon pair sources, after erasing the photon's which-path information. In order to certify the entanglement, we use an entanglement witness which does not rely on post-selection. We herald entanglement between two locations, separated by a total distance of 2 km of optical fiber, at a rate of 1.6 kHz. This work paves the way towards high-rate and practical quantum repeater architectures.Comment: 5+9 pages, 7 figure

CERN Summer Student Programme Report by Misael CALOZ

The aim of this report is to give an overview of my work during the summer student programme at CERN. My project was a work of 8 weeks (16/06 to 8/08 2014) in the Radiation Protection group of the Occupational Health & Safety and Environmental Protection Unit and was supervised by M. Robert Froeschl

Superconducting nanowire single-photon detectors for quantum communication applications

La technologie des détecteurs de photon unique a suscité un intérêt croissant au cours de la dernière décennie. Une des raisons majeures de cette tendance sont les applications en communication quantique, telles que la distribution de clés quantiques, qui nécessitent des détecteurs à hautes performances. Les détecteurs de photon unique à nanofils supraconducteurs (SNSPD) sont sensibles aux photons uniques aux longueurs d’onde allant des rayons X jusqu’à l’infrarouge moyen et offrent des performances inégalées sur de nombreux aspects. Ils présentent généralement des efficacités très élevées sur une large gamme de longueurs d’onde, ainsi qu’un faible bruit, une gigue temporelle faible, et un taux de répétition élevé. Le travail présenté dans cette thèse couvre tous les aspects essentiels des SNSPDs fabriqués en molybdène-silicium (MoSi). Alors que la nano-fabrication, la caractérisation, la recherche des limites intrinsèques et le mécanisme de détection constituent le cœur de ce travail, la motivation principale à l’origine de cette thèse a toujours été de fournir des détecteurs de photon unique performants pour des applications de communication quantique exigeantes effectuées au sein même du groupe. Malgré un grand nombre de travaux expérimentaux visant à améliorer les performances des SNSPD depuis leur invention, une description complète du mécanisme de détection n’a pas encore été établie. La motivation principale de la première partie de cette thèse est d’apporter une réponse à cette question. Les hautes performances obtenues sont discutées dans la deuxième partie de ce manuscrit, où sont présentés des détecteurs combinant une efficacité de détection élevée (> 85 %) et une gigue temporelle faible (<30 ps). La troisième partie de cette thèse porte sur l’étude des limites intrinsèques et fondamentales de la gigue temporelle, en partie réalisée au Jet Propulsion Laboratory de la NASA (USA). Notre travail a notamment montré qu’il existe un compromis entre la gigue temporelle, le courant de verrouillage, l’inductance cinétique et, par conséquent, l’efficacité des détecteurs. Après avoir optimisé le rapport signal sur bruit en réglant les inductances cinétiques en série tout en contrôlant l’effet de verrouillage, nous avons obtenu une gigue temporelle minimale de 6.0 ps à 532 nm et de 10.6 ps à 1550 nm. Enfin, des résultats très récents et prometteurs sur le taux de comptage maximum sont présentés en dernière partie. Les résultats préliminaires sur des détecteurs fabriqués à partir de nitrure de niobium-titane (NbTiN) sont également discutés, ouvrant la porte à de nouvelles opportunités et améliorations dans le domaine des SNSPD

Direct measurement of the recovery time of superconducting nanowire single-photon detectors

One of the key properties of single-photon detectors is their recovery time, i.e. the time required for the detector to recover its nominal efficiency. In the case of superconducting nanowire single-photon detectors (SNSPDs), which can feature extremely short recovery times in free-running mode, a precise characterization of this recovery time and its time dynamics is essential for many quantum optics or quantum communication experiments. We introduce a fast and simple method to characterize precisely the recovery time of SNSPDs. It provides full information about the recovery of the efficiency in time for a single or several consecutive detections. We also show how the method can be used to gain insight into the behavior of the bias current inside the nanowire after a detection, which allows predicting the behavior of the detector and its efficiency in any practical experiment using these detectors

Operation of parallel SNSPDs at high detection rates

Recent progress in the development of superconducting nanowire single-photon detectors (SNSPD) has delivered excellent performance, and their increased adoption has had a great impact on a range of applications. One of the key characteristic of SNSPDs is their detection rate, which is typically higher than other types of free-running single-photon detectors. The maximum achievable rate is limited by the detector recovery time after a detection, which itself is linked to the superconducting material properties and to the geometry of the meandered SNSPD. Arrays of detectors biased individually can be used to solve this issue, but this approach significantly increases both the thermal load in the cryostat and the need for time processing of the many signals, and this scales unfavorably with a large number of detectors. One potential scalable approach to increase the detection rate of individual detectors further is based on parallelizing smaller meander sections. In this way, a single detection temporarily disables only one subsection of the whole active area, thereby leaving the overall detection efficiency mostly unaffected. In practice however, cross-talk between parallel nanowires typically leads to latching, which prevents high detection rates. Here we show how this problem can be avoided through a careful design of the whole SNSPD structure. Using the same electronic readout as with conventional SNSPDs and a single coaxial line, we demonstrate detection rates over 200 MHz without any latching, and a fibre-coupled SDE as high as 77%, and more than 50% average SDE per photon at 50 MHz detection rate under continuous wave illumination

Intrinsically-limited timing jitter in molybdenum silicide superconducting nanowire single-photon detectors

Recent progress in the development of superconducting nanowire single-photon detectors (SNSPDs) has delivered excellent performance and has had a great impact on a range of research fields. The timing jitter, which denotes the temporal resolution of the detection, is a crucial parameter for many applications. Despite extensive work since their apparition, the lowest jitter achievable with SNSPDs is still not clear, and the origin of the intrinsic limits is not fully understood. Understanding its intrinsic behavior and limits is a mandatory step toward improvements. Here, we report our experimental study on the intrinsically-limited timing jitter in molybdenum silicide SNSPDs. We show that to reach intrinsic jitter, crucial properties such as the latching current and the kinetic inductance of the devices have to be understood. The dependence on the nanowire thickness and the energy dependence of the intrinsic jitter are quantified, and the origin of the limits is exhibited. System timing jitter of 6.0 ps at 532 nm and 10.6 ps at 1550 nm photon wavelength has been obtained