R. Leoni - Academia.edu (original) (raw)
Papers by R. Leoni
AIP Conference Proceedings, 2006
We show a tunable flux qubit with built‐in readout, realized with a double SQUID with a supplemen... more We show a tunable flux qubit with built‐in readout, realized with a double SQUID with a supplementary Josephson junction. State preparation and manipulation of the qubit are achieved by applying pulses of magnetic flux in two externally coupled coils, a feature that suits very well with a future integration with RSFQ integrated logic. We show how the system can be read out and prepared in a definite flux state, moreover we show the results of manipulation (lowering of the potential barrier between states) in incoherent regime at ...
Optical Complex Systems: OCS11, 2011
The implementation of single-photon detectors in waveguide photonic circuits will open the possib... more The implementation of single-photon detectors in waveguide photonic circuits will open the possibility of experiments in quantum regime that would otherwise be impossible to be implemented using bulk optics. Nanowire superconducting single-photon detectors (SSPDs) are good candidates for integration due to their relative ease of fabrication on top of GaAs heterostructures. In this paper we show the experimental demonstration of single-photon detectors, based on superconducting nanowires, fully integrated with GaAs/AlGaAs ridge waveguides. We will discuss all the major challenges surmounted and all the steps necessary to achieve these results.
Quantum Computing in Solid State Systems, 2006
Superconducting devices based on the Josephson effect are promising candidates for the implementa... more Superconducting devices based on the Josephson effect are promising candidates for the implementation of quantum computing. After the experimental demonstration of the coherent manipulation and coupling of Josephson qubits1-8, the actual efforts concern the design and realization of new optimised elements with small decoherence, efficient readout, simple and complete coherent manipulation, integration and coupling of more qubits. In this direction we have realized a double SQUID qubit with a fully gradiometric configuration ...
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
Abstract Study of subwavelength optical phenomena has taken an increasing importance in the past ... more Abstract Study of subwavelength optical phenomena has taken an increasing importance in the past few years. Near-field scanning optical microscopy (NSOM) is the usual solution for optical sensing below the diffraction limit. It consists in coupling light in a fiber through a nanoscale hole and detecting it with a conventional detector. A better optimized method would be to make the detector itself nanoscale. The dark count rate being usually proportional to the active area, this would greatly enhance the signal to noise ratio. The ...
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
Abstract A superconducting bolometer with an on-chip lithographic terahertz antenna has been char... more Abstract A superconducting bolometer with an on-chip lithographic terahertz antenna has been characterized in passive and active mode. Direct detection measurements made with 300K/77K blackbody sources yeld an optical efficiency of 10%. Time response of the bolometer has been obtained at 2.5 and 4.4 THz by illuminating the detector with quantum cascade lasers (QCL) showing a time constant of 1.2 μs. Here we report on the fabrication and the optical characterization of an antenna-coupled hot-spot microbolometer operating ...
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
Abstract Active spectroscopic imaging is based on arrays of broadband, short-response-time detect... more Abstract Active spectroscopic imaging is based on arrays of broadband, short-response-time detectors observing a scene illuminated by a number of THz sources. Here we present the system design, the fabrication process and the single-pixel test for three detector technologies: GaAs Schottky diodes, GaN transistors, Nb bolometers.
Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2009
We show how the parallel connection of photo-sensitive supercon-ducting nanowires can be used to ... more We show how the parallel connection of photo-sensitive supercon-ducting nanowires can be used to count the number of photons in an optical pulse, down to the single-photon level. Using this principle we demonstrate photon-number resolving detectors with unprecedented sensitivity and speed at telecommunication wavelengths.
Recent Optical and Photonic Technologies, 2010
Source: Recent Optical and Photonic Technologies, Book edited by: Ki Young Kim, ISBN 978-953-7619... more Source: Recent Optical and Photonic Technologies, Book edited by: Ki Young Kim, ISBN 978-953-7619-71-8, pp. 450, January 2010, INTECH, Croatia, downloaded from SCIYO.COM
Macroscopic Quantum Coherence and Quantum Computing, 2001
ABSTRACT A superconducting single electron transistor, based on aluminum electrodes, was fabricat... more ABSTRACT A superconducting single electron transistor, based on aluminum electrodes, was fabricated and studied. The characterization was made by measuring both the transport properties as a function of temperature and the noise performance. As a result, we observed modulation of the transfer characteristics up to 1.4K and we measured a charge sensitivity of 3.8 10-4 e/√Hz at 10 Hz and 0.3 K.
Optics Express, 2012
We present an experimental method to characterize multiphoton detectors with a small overall dete... more We present an experimental method to characterize multiphoton detectors with a small overall detection efficiency. We do this by separating the nonlinear action of the multiphoton detection event from linear losses in the detector. Such a characterization is a necessary step for quantum information protocols with single and multiphoton detectors and can provide quantitative information to understand the underlying physics of a given detector. This characterization is applied to a superconducting multiphoton nanodetector, consisting of an NbN nanowire with a bowtie-shaped subwavelength constriction. Depending on the bias current, this detector has regimes with single and multiphoton sensitivity. We present the first full experimental characterization of such a detector.
2014 Fotonica AEIT Italian Conference on Photonics Technologies, 2014
ABSTRACT A novel photon-number-resolving detector (PNRD) structure, based on an array of nanowire... more ABSTRACT A novel photon-number-resolving detector (PNRD) structure, based on an array of nanowire superconducting single photon detectors (SSPDs) connected in series, have recently been proposed. With this configuration, it is possible to scale to large photon numbers. In this framework, PNRDs capable of resolving up to four, eight and twelve photons at telecommunication wavelengths have been fabricated and tested. The photon-induced voltage signals from all the series elements are summed up into a single readout pulse with a height proportional to the detected photon number. Analysis of the linearity shows the potential of scaling to an even larger dynamic range.
Conference on Lasers and Electro-Optics 2012, 2012
We present a novel approach to an ultrafast N-photon autocorrelator with single-photon sensitivit... more We present a novel approach to an ultrafast N-photon autocorrelator with single-photon sensitivity based on superconducting nanodetectors. The hotspot relaxation time which determines the autocorrelator's temporal resolution was measured to be ~20 ps.
Conference on Lasers and Electro-Optics 2012, 2012
ABSTRACT We present a novel photon number resolving detector based on the series array of superco... more ABSTRACT We present a novel photon number resolving detector based on the series array of superconducting nanowires, each shunted by an integrated resistor. The device can successfully discriminate between 1-4 absorbed photons in telecom-wavelength optical pulses.
Advanced Photon Counting Techniques VI, 2012
We present a novel configuration for a photon number resolving detector based on a series array o... more We present a novel configuration for a photon number resolving detector based on a series array of shunted superconducting nanowires, which has the potential to provide a high dynamic range. The first prototype of the detector consisting of four series elements is demonstrated with the ability to resolve up to four photons in an incident optical pulse at the telecommunication wavelength window.
2013 IEEE Photonics Conference, 2013
ABSTRACT We present a quantum integrated photonics platform on GaAs including waveguide single-ph... more ABSTRACT We present a quantum integrated photonics platform on GaAs including waveguide single-photon sources and detectors on the same chip.
In the framework of a near-IR monitoring program of EXor pre-Main sequence variables (Lorenzetti ... more In the framework of a near-IR monitoring program of EXor pre-Main sequence variables (Lorenzetti et al. 2007 ApJ 665, 1182; Lorenzetti et al. 2009 ApJ 693, 1056) we are carrying out at the AZT24 1m IR telescope (Campo Imperatore, Italy), we have observed the recent outburst of HBC 722 (ATel #2801) located in NGC 7000/IC 5070. Low resolution spectroscopy in the optical band (ATel #2808) and subsequent follow-up photometry in the BVRI bands (ATel #2819) have confirmed the nature of this object as to be similar to FU Orionis sources.
Physical Review Letters, 2007
We report on experiments performed to probe quantum coherence between the two potential wells of ... more We report on experiments performed to probe quantum coherence between the two potential wells of a double SQUID system in the absence of external rf-signals. The system consists essentially of an rf-SQUID in which the Josephson junction interrupting the superconducting loop is replaced by another (smaller) loop containing two junctions in parallel. Experimental evidence at temperatures of the order of 10 mK shows that the system may develop three potential energy wells, which modify the usual two well energy profile and thereby vanify the qubit manipulation strategy. Analysis shows that the appearance of the third potential well can be interpreted as evidence of a butterfly catastrophe, namely a catastrophe expected for a system described by four control parameters and one state variable. The experimental results are interpreted on the basis of projections of the folded behaviour surface in the planes of the experimental control parameters.
Physical Review Letters, 2013
We demonstrate a novel method to measure Nth-order (N ¼ 1; 2; 3; 4) interferometric autocorrelati... more We demonstrate a novel method to measure Nth-order (N ¼ 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 quasiparticle 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.
Physical Review B, 2005
Magnetotransport measurements revealing signatures of ballistic transport effects in strained sil... more Magnetotransport measurements revealing signatures of ballistic transport effects in strained silicon cavities are presented. We will discuss magnetic focusing occurring at low magnetic fields and the presence of a negative magnetoresistance peak akin to the weak localization structures. Both effects have been intensively investigated in GaAs/AlGaAs systems but, to the best of our knowledge, this is the first observation in SiGe heterostructures [1]- .
AIP Conference Proceedings, 2006
We show a tunable flux qubit with built‐in readout, realized with a double SQUID with a supplemen... more We show a tunable flux qubit with built‐in readout, realized with a double SQUID with a supplementary Josephson junction. State preparation and manipulation of the qubit are achieved by applying pulses of magnetic flux in two externally coupled coils, a feature that suits very well with a future integration with RSFQ integrated logic. We show how the system can be read out and prepared in a definite flux state, moreover we show the results of manipulation (lowering of the potential barrier between states) in incoherent regime at ...
Optical Complex Systems: OCS11, 2011
The implementation of single-photon detectors in waveguide photonic circuits will open the possib... more The implementation of single-photon detectors in waveguide photonic circuits will open the possibility of experiments in quantum regime that would otherwise be impossible to be implemented using bulk optics. Nanowire superconducting single-photon detectors (SSPDs) are good candidates for integration due to their relative ease of fabrication on top of GaAs heterostructures. In this paper we show the experimental demonstration of single-photon detectors, based on superconducting nanowires, fully integrated with GaAs/AlGaAs ridge waveguides. We will discuss all the major challenges surmounted and all the steps necessary to achieve these results.
Quantum Computing in Solid State Systems, 2006
Superconducting devices based on the Josephson effect are promising candidates for the implementa... more Superconducting devices based on the Josephson effect are promising candidates for the implementation of quantum computing. After the experimental demonstration of the coherent manipulation and coupling of Josephson qubits1-8, the actual efforts concern the design and realization of new optimised elements with small decoherence, efficient readout, simple and complete coherent manipulation, integration and coupling of more qubits. In this direction we have realized a double SQUID qubit with a fully gradiometric configuration ...
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
Abstract Study of subwavelength optical phenomena has taken an increasing importance in the past ... more Abstract Study of subwavelength optical phenomena has taken an increasing importance in the past few years. Near-field scanning optical microscopy (NSOM) is the usual solution for optical sensing below the diffraction limit. It consists in coupling light in a fiber through a nanoscale hole and detecting it with a conventional detector. A better optimized method would be to make the detector itself nanoscale. The dark count rate being usually proportional to the active area, this would greatly enhance the signal to noise ratio. The ...
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
Abstract A superconducting bolometer with an on-chip lithographic terahertz antenna has been char... more Abstract A superconducting bolometer with an on-chip lithographic terahertz antenna has been characterized in passive and active mode. Direct detection measurements made with 300K/77K blackbody sources yeld an optical efficiency of 10%. Time response of the bolometer has been obtained at 2.5 and 4.4 THz by illuminating the detector with quantum cascade lasers (QCL) showing a time constant of 1.2 μs. Here we report on the fabrication and the optical characterization of an antenna-coupled hot-spot microbolometer operating ...
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
Abstract Active spectroscopic imaging is based on arrays of broadband, short-response-time detect... more Abstract Active spectroscopic imaging is based on arrays of broadband, short-response-time detectors observing a scene illuminated by a number of THz sources. Here we present the system design, the fabrication process and the single-pixel test for three detector technologies: GaAs Schottky diodes, GaN transistors, Nb bolometers.
Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2009
We show how the parallel connection of photo-sensitive supercon-ducting nanowires can be used to ... more We show how the parallel connection of photo-sensitive supercon-ducting nanowires can be used to count the number of photons in an optical pulse, down to the single-photon level. Using this principle we demonstrate photon-number resolving detectors with unprecedented sensitivity and speed at telecommunication wavelengths.
Recent Optical and Photonic Technologies, 2010
Source: Recent Optical and Photonic Technologies, Book edited by: Ki Young Kim, ISBN 978-953-7619... more Source: Recent Optical and Photonic Technologies, Book edited by: Ki Young Kim, ISBN 978-953-7619-71-8, pp. 450, January 2010, INTECH, Croatia, downloaded from SCIYO.COM
Macroscopic Quantum Coherence and Quantum Computing, 2001
ABSTRACT A superconducting single electron transistor, based on aluminum electrodes, was fabricat... more ABSTRACT A superconducting single electron transistor, based on aluminum electrodes, was fabricated and studied. The characterization was made by measuring both the transport properties as a function of temperature and the noise performance. As a result, we observed modulation of the transfer characteristics up to 1.4K and we measured a charge sensitivity of 3.8 10-4 e/√Hz at 10 Hz and 0.3 K.
Optics Express, 2012
We present an experimental method to characterize multiphoton detectors with a small overall dete... more We present an experimental method to characterize multiphoton detectors with a small overall detection efficiency. We do this by separating the nonlinear action of the multiphoton detection event from linear losses in the detector. Such a characterization is a necessary step for quantum information protocols with single and multiphoton detectors and can provide quantitative information to understand the underlying physics of a given detector. This characterization is applied to a superconducting multiphoton nanodetector, consisting of an NbN nanowire with a bowtie-shaped subwavelength constriction. Depending on the bias current, this detector has regimes with single and multiphoton sensitivity. We present the first full experimental characterization of such a detector.
2014 Fotonica AEIT Italian Conference on Photonics Technologies, 2014
ABSTRACT A novel photon-number-resolving detector (PNRD) structure, based on an array of nanowire... more ABSTRACT A novel photon-number-resolving detector (PNRD) structure, based on an array of nanowire superconducting single photon detectors (SSPDs) connected in series, have recently been proposed. With this configuration, it is possible to scale to large photon numbers. In this framework, PNRDs capable of resolving up to four, eight and twelve photons at telecommunication wavelengths have been fabricated and tested. The photon-induced voltage signals from all the series elements are summed up into a single readout pulse with a height proportional to the detected photon number. Analysis of the linearity shows the potential of scaling to an even larger dynamic range.
Conference on Lasers and Electro-Optics 2012, 2012
We present a novel approach to an ultrafast N-photon autocorrelator with single-photon sensitivit... more We present a novel approach to an ultrafast N-photon autocorrelator with single-photon sensitivity based on superconducting nanodetectors. The hotspot relaxation time which determines the autocorrelator's temporal resolution was measured to be ~20 ps.
Conference on Lasers and Electro-Optics 2012, 2012
ABSTRACT We present a novel photon number resolving detector based on the series array of superco... more ABSTRACT We present a novel photon number resolving detector based on the series array of superconducting nanowires, each shunted by an integrated resistor. The device can successfully discriminate between 1-4 absorbed photons in telecom-wavelength optical pulses.
Advanced Photon Counting Techniques VI, 2012
We present a novel configuration for a photon number resolving detector based on a series array o... more We present a novel configuration for a photon number resolving detector based on a series array of shunted superconducting nanowires, which has the potential to provide a high dynamic range. The first prototype of the detector consisting of four series elements is demonstrated with the ability to resolve up to four photons in an incident optical pulse at the telecommunication wavelength window.
2013 IEEE Photonics Conference, 2013
ABSTRACT We present a quantum integrated photonics platform on GaAs including waveguide single-ph... more ABSTRACT We present a quantum integrated photonics platform on GaAs including waveguide single-photon sources and detectors on the same chip.
In the framework of a near-IR monitoring program of EXor pre-Main sequence variables (Lorenzetti ... more In the framework of a near-IR monitoring program of EXor pre-Main sequence variables (Lorenzetti et al. 2007 ApJ 665, 1182; Lorenzetti et al. 2009 ApJ 693, 1056) we are carrying out at the AZT24 1m IR telescope (Campo Imperatore, Italy), we have observed the recent outburst of HBC 722 (ATel #2801) located in NGC 7000/IC 5070. Low resolution spectroscopy in the optical band (ATel #2808) and subsequent follow-up photometry in the BVRI bands (ATel #2819) have confirmed the nature of this object as to be similar to FU Orionis sources.
Physical Review Letters, 2007
We report on experiments performed to probe quantum coherence between the two potential wells of ... more We report on experiments performed to probe quantum coherence between the two potential wells of a double SQUID system in the absence of external rf-signals. The system consists essentially of an rf-SQUID in which the Josephson junction interrupting the superconducting loop is replaced by another (smaller) loop containing two junctions in parallel. Experimental evidence at temperatures of the order of 10 mK shows that the system may develop three potential energy wells, which modify the usual two well energy profile and thereby vanify the qubit manipulation strategy. Analysis shows that the appearance of the third potential well can be interpreted as evidence of a butterfly catastrophe, namely a catastrophe expected for a system described by four control parameters and one state variable. The experimental results are interpreted on the basis of projections of the folded behaviour surface in the planes of the experimental control parameters.
Physical Review Letters, 2013
We demonstrate a novel method to measure Nth-order (N ¼ 1; 2; 3; 4) interferometric autocorrelati... more We demonstrate a novel method to measure Nth-order (N ¼ 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 quasiparticle 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.
Physical Review B, 2005
Magnetotransport measurements revealing signatures of ballistic transport effects in strained sil... more Magnetotransport measurements revealing signatures of ballistic transport effects in strained silicon cavities are presented. We will discuss magnetic focusing occurring at low magnetic fields and the presence of a negative magnetoresistance peak akin to the weak localization structures. Both effects have been intensively investigated in GaAs/AlGaAs systems but, to the best of our knowledge, this is the first observation in SiGe heterostructures [1]- .