Photon-number resolving detector based on a series array of superconducting nanowires

We present the experimental demonstration of a superconducting photon number resolving detector. It is based on the series connection of N superconducting nanowires, each connected in parallel to an integrated resistor. The device provides a single voltage readout, proportional to the number of photons absorbed in distinct nanowires. Clearly separated output levels corresponding to the detection of n=1-4 photons are observed in a 4-element detector fabricated from an NbN film on GaAs substrate, with a single-photon system quantum efficiency of 2.6% at the wavelength of 1300nm. The series-nanowire structure is promising in view of its scalability to large photon numbers and high efficiencies.Comment: 12 pages, 6 figure

Ultrasensitive N-photon interferometric autocorrelator

We demonstrate a novel method to measure the Nth-order (N=1, 2, 3, 4) interferometric autocorrelation with high sensitivity and temporal resolution. It is based on the combination of linear absorption and nonlinear detection in a superconducting nanodetector, providing much higher efficiency than methods based on all-optical nonlinearities. Its temporal resolution is only limited by the quasi-particle energy relaxation time, which is directly measured to be in the 20 ps range for the NbN films used in this work. We present a general model of interferometric autocorrelation with these nonlinear detectors and discuss the comparison with other approaches and possible improvements

Superconducting series nanowire detector counting up to twelve photons

We demonstrate a superconducting photon-number-resolving detector capable of resolving up to twelve photons at telecommunication wavelengths. It is based on a series array of twelve superconducting NbN nanowire elements, each connected in parallel with an integrated resistor. The photon-induced voltage signals from the twelve elements are summed up into a single readout pulse with a height proportional to the detected photon number. Thirteen distinct output levels corresponding to the detection of n=0-12 photons are observed experimentally. A detailed analysis of the excess noise shows the potential of scaling to an even larger dynamic range.Comment: 13 page

Ultra-subwavelength resonators for high temperature high performance quantum detectors

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Waveguide single-photon detectors for integrated quantum photonic circuits

The generation, manipulation and detection of quantum bits (qubits) encoded on single photons is at the heart of quantum communication and optical quantum information processing. The combination of single-photon sources, passive optical circuits and single-photon detectors enables quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. However, the monolithic integration of sources, waveguides and detectors on the same chip, as needed for scaling to meaningful number of qubits, is very challenging, and previous work on quantum photonic circuits has used external sources and detectors. Here we propose an approach to a fully-integrated quantum photonic circuit on a semiconductor chip, and demonstrate a key component of such circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (20%) at telecom wavelengths, high timing accuracy (60 ps), response time in the ns range, and are fully compatible with the integration of single-photon sources, passive networks and modulators.Comment: 11 pages, 4 figure

Conductance anomalies in quantum point contacts

We present a study of the conductance of quantum point contacts fabricated in AlGaN/GaN and Si/SiGe heterostructures. The investigated devices differ for typology (split gates and etched devices, respectively) and for the resulting potential profiles. We observe conductance quantization in multiple of 2e2/h units with superimposed anomalous plateaus and/or structures suggesting that correlation effects should be included in the description of our 1D systems

Quantum transport in low-dimensional Si/SiGe and AlGaN/GaN systems

In recent years the study of electronic properties of low dimensional mesoscopic systems has attracted considerable interest. One of the reasons for this is the opportunity it gives of investigating a wide range of new effects related to ballistic transport and phase coherence. Another reason can be found in the possibility it gives of fabricating nanostructures both for microelectronics and for possible applications in quantum computing and spintronics in general. The object of this thesis is the investigation of quantum transport in Si/SiGe- and AlGaN/GaN -based Quantum Point Contacts (QPCs). In particular, we focus on ballistic transport effects going beyond the oneelectron Landauer picture expected for a system of non-interacting electrons. Si-based nanostructures are one of the most important material systems for applications in spintronics and quantum information due to the weak spinorbit coupling and to the presence of nuclear zero spin isotopes, which make electron spin coherence time extremely long. However, silicon has a near degeneracy of orbital states in the conduction band, arising from multiple valley minima, which can enhance decoherence rates and make qubit operation in quantum computing more complicated. It has been shown that quantum confinement in nanostructures provides some amount of control over the valley splitting [1]. In this work, we have investigated quantum transport properties of strongly-confined Shottky-gated constrictions, made starting from Si-based 2DEG and focusing on the conductance behaviour of nanostructures with various geometries. Measurements have been made as a function of the gate voltage, the source-drain bias and the magnetic field. Our results reveal a complex framework due to the occurrence of deviations from the ideal quantized conductance behaviour. For instance, these can be due to backscat1 tering from impurities or transmission resonances, produced by multiple reflections, for the presence of an abrupt geometry of the confining potential. However our findings have revealed a zero-field energy valley splitting in our etched-nanostructures, due to the strong confinement generated by physical etching of the 2DEG heterostructures. In practice, in different devices we found a valley splitting energy of the order of ∼ 1meV that is comparable to values reported in literature. In the past ten years, due to developments in the field of AlGaN/GaN heterostructures, research has focused also on GaN -based 2DEG. The latter is in fact among the most promising materials for the study of properties related to ballistic transport and it is interesting from a technological point of view. GaN -based 2DEGs are a novel system in which the large band offset and the strong piezoelectric effect in this material system have been shown to generate an intrinsic high sheet density two-dimensional electron gas, ns ∼ 1013 cm−2 in our sample, with enhanced electron mobility [2, 3]. In addition, the relatively heavy mass of electrons makes GaN 2DEGs a convenient system for studying spin-polarized and electron-electron correlation effects. The strong spontaneous and piezoelectric polarization charge gives these systems a strong asymmetric electric field at the interface, which can also enhance the spin-orbit interaction, thus providing a spin-splitting energy of the conduction band states at zero-external field [4]. In this thesis we focused on the study of the electrical properties of an AlGaN/GaN 2DEG-system, exploiting both classical and quantum Hall effect. In our investigation, new interesting problems came out from the analysis of both Shubnikov-de Haas and low-field measurements: the occupancy of a second energy level of the 2DEG, the occurrence of a zero-field spinsplitting due to spin-orbit interaction and the occurrence of the key-feature of weak antilocalization [5], namely positive magnetoresistance. Electron quantum transport of mesoscopic devices on GaN -based heterostructures was also investigated. For these systems we measured the conductance as a function of the gate voltage and the magnetic field. In addition, we investigated the effect of deliberately introducing an asymmetry in the confining potential. We have obtained an interesting and rich framework in which we speculate the possibility of a zero-field spin-polarization as being due to the effect of asymmetry of the confining potential and the presence of a spin- 2 orbit coupling [6]. References [1] S. Goswami, K. A. Slinker, M. Friesen, L. M. McGuire, J. L. Truitt, C. Tahan, L. J. Klein, J. O. Chu, P. M. Mooney, D. W. van der Wiede, R. Joynt, S. N. Coppersmith, and M. A. Eriksson, Nature Physics 3 (2007), 41. [2] O. Ambacher, B. Foutz, J. Smart, J. R. Shealy, N. G. Weimann, K. Chu, M. Murphy, A. J. Sierakowski, W. J. Schaff, L. F. Eastman, R. Dimitrov, A. Mitchell, and M. Stutzmann, J. Appl. Phys. 87 (2000), 334. [3] A. D. Bykhovski, R. Gaska, and M. S. Shur, Appl. Phys. Lett. 72 (1998), 3577. [4] S. Schmult, M. J. Manfra, A. Punnoose, A. M. Sergent, K. W. Baldwin, and R. J. Molnar, Phys. Rev. B 74 (2006), 03302. [5] A. E. Belyaev, V. G. Raicheva, A. M. Kurakin, N. Klein, and S. A. Vitusevich, Phys. Rev. B 77 (2008), 035311. [6] P. Debray, S. M. Rahman, J. Wan, R. S. Newrock, M. Cahay, A. T. Ngo, S. E. Ulloa, S. T. Herbert, M. Muhammad, and M. Johnson, Nature Nanotechnology advance online publication (2009)

Development of Methods for Recovering Endotoxins from Surfaces and from Air in Production Environment of Injectable Drugs

The aim of this work is to develop and validate methods for quantifying endotoxins on surfaces and in the air of the manufacturing environment of injectable drugs, in order to use them to evaluate the quality of the process and the risk for the products processed therein. The method for recovering endotoxins from surfaces is a direct method that provides sampling surfaces by swabbing and extraction of endotoxins from the swabs with an appropriate diluent, while the method for airborne endotoxins provides an air-active sampling on a glass fiber filter and endotoxins extraction with an appropriate diluent.LAY ABSTRACT: Bacterial endotoxins are present in the environments devoted to the manufacturing of injectable drugs and could be a real risk for the quality and the safety of such drugs. So the quality control laboratories should have analytical methods to recover bacterial endotoxins from environmental samples. The aim of this publication is to show how we succeeded in developing and validating methods to quantify bacterial endotoxins on surfaces and in the air

Integrated autocorrelator based on superconducting nanowires

This work was financially supported by the European Commission through FP7 QUANTIP (Contract No. 244026)We demonstrate an integrated autocorrelator based on two superconducting single-photon detectors patterned on top of a GaAs ridge waveguide. This device enables the on-chip measurement of the second-order intensity correlation function g((2))(tau). A polarization-independent device quantum efficiency in the 1% range is reported, with a timing jitter of 88 ps at 1300 nm. g((2))(tau) measurements of continuous-wave and pulsed laser excitations are demonstrated with no measurable crosstalk within our measurement accuracy. © 2013 OSA.Publisher PDFPeer reviewe