Guido Torrioli | Consiglio Nazionale delle Ricerche (CNR) (original) (raw)

Papers by Guido Torrioli

Page 1. F. Chiarello1, P. Carelli2, MG Castellano1, C. Cosmelli3, R. Leoni1, F. Mattioli1, S. Pol... more Page 1. F. Chiarello1, P. Carelli2, MG Castellano1, C. Cosmelli3, R. Leoni1, F. Mattioli1, S. Poletto1, D. Simeone1, G. Torrioli1 1) INFN and Istituto di Fotonica e Nanotecnologie - CNR, via Cineto Romano 42, 00156 Roma 2) INFN andUniversità dell'Aquila, Monteluco di Roio, 67040 L'Aquila 3) INFN and Università di Roma “La Sapienza”, P.le A. Moro 2, 00185 Roma Superconducting Josephson Elements for Quantum Computing Page 2.

Abstract We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junction... more Abstract We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junctions made by a thin film of heavily doped silicon in contact with superconducting electrodes through Schottky barriers. Doped silicon films were chemical vapor deposited on silicon-on-insulator substrates and laterally dry etched in mesas. Aluminum or, alternatively, niobium contacts were deposited on the mesas.

Abstract We describe a simple and efficient scheme for the readout of a tunable flux qubit, and p... more Abstract We describe a simple and efficient scheme for the readout of a tunable flux qubit, and present preliminary experimental tests for the preparation, manipulation and final readout of the qubit state, performed in the incoherent regime at liquid helium temperature.

Abstract The flux states of a rf superconducting quantum interference device (SQUID) can be used ... more Abstract The flux states of a rf superconducting quantum interference device (SQUID) can be used to investigate macroscopic quantum effects, the most challenging of which is the detection of quantum coherent oscillations, and are promising candidates for the implementation of quantum computing. The use of a proper readout system is of utmost importance for these purposes.

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.

One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA a... more One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor thermometers. The pixels have metallic X-ray absorbers and are read-out by multiplexed SQUID electronics. The requirements for this instrument are demanding.

Abstract We introduce a three-junction superconducting quantum interference device (SQUID) that c... more Abstract We introduce a three-junction superconducting quantum interference device (SQUID) that can be used as an optimal tunable element in Josephson quantum computing applications. This device can replace the simple dc SQUID generally used as a tunable element in this kind of applications, with a series of advantages concerning the coherence time and the tolerance to small errors. We study the device both theoretically and experimentally at 4.2 K, obtaining a good agreement between the results.

We have investigated the pair tunneling process in step-edge Josephson junctions by studying the ... more We have investigated the pair tunneling process in step-edge Josephson junctions by studying the lifetime of the metastable zero-voltage state determined by the thermal activation out of the potential well. The junctions have a hysteretic current–voltage characteristic at 4.2 K, which allows the recording of transitions and switching distribution from the Josephson current to the resistive state. By applying an external magnetic field, we have found a strong dependence of the activation energy on the field intensity.

Abstract We present a methodology of network data analysis applied to the search for coincident b... more Abstract We present a methodology of network data analysis applied to the search for coincident burst excitations over a 24 h long data set collected by AURIGA, EXPLORER, NAUTILUS and Virgo detectors during September 2005. The search of candidate triggers was performed independently on each of the data sets from single detectors. We looked for two-fold time coincidences between these candidates using an algorithm optimized for a given population of sources

We report on experiments performed to probe quantum coherence in a system consisting of an rf-SQU... more We report on experiments performed to probe quantum coherence in a system consisting of an rf-SQUID in which the Josephson junction is replaced by a small loop containing two junctions in parallel. At temperatures of the order of 10 mK the system may develop three potential energy wells, which modify the usual two well energy profile and thereby verify the qubit manipulation strategy.

bicrystal dc-superconducting quantum interference devices (SQUIDs) and single layer magnetometers... more bicrystal dc-superconducting quantum interference devices (SQUIDs) and single layer magnetometers working at 77 K have been fabricated and analyzed. Samples have been made in situ by cylindrical magnetron dc sputtering on [001] bicrystal substrates. Magnetic flux noise levels and magnetic field sensitivities by standard flux-locked-loop electronics have been measured out on dc-SQUIDs and magnetometers, respectively.

Abstract We discuss and demonstrate a prototype of superconducting transformer with a flux transf... more Abstract We discuss and demonstrate a prototype of superconducting transformer with a flux transfer function that can be varied in a wide range, by acting on a control parameter.

Abstract The dc-superconducting quantum interference device (SQUID) is a low-noise converter from... more Abstract The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit of ħ/2. A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve.

Abstract We cooled down the electrons of a 3 μm 3 copper strip by using an on-chip electronic mic... more Abstract We cooled down the electrons of a 3 μm 3 copper strip by using an on-chip electronic microcooler made by a superconductor-insulator-normal-insulator-superconductor (SINIS) structure. We obtained an electron temperature drop ΔT≃-10 mK at a temperature of the bath slightly above T b= 500 mK and we estimated a cooling power slightly larger than 20 pW at this temperature. In contrast to previous experiments, we obtained this result operating with a simple 3 He refrigerator.

Abstract The data collected during 2005 by the resonant bar Explorer are divided into segments an... more Abstract The data collected during 2005 by the resonant bar Explorer are divided into segments and incoherently summed in order to perform an all-sky search for periodic gravitational wave signals. The parameter space of the search spanned about 40 Hz in frequency, over 23927 positions in the sky. Neither source orbital corrections nor spindown parameters have been included, with the result that the search was sensitive to isolated neutron stars with a frequency drift less than 6× 10− 11 Hz s− 1.

Abstract We present an experimental study on the retrapping process of a hysteretic, high-quality... more Abstract We present an experimental study on the retrapping process of a hysteretic, high-quality Josephson junction; namely, we have measured the distribution of the values at which the junction switches back from the voltage state to the zero-voltage state, as a function of the applied magnetic field. While the opposite process (escape from the zero-voltage state) has been extensively studied in the past, both from the theoretical and the experimental point of view, little is found in the literature on the retrapping process.

We present measurements of the supercurrent decay in high quality Nb/AlOx/Nb Josephson junctions ... more We present measurements of the supercurrent decay in high quality Nb/AlOx/Nb Josephson junctions which show evidence of energy-level quantization within the washboard potential describing the junction. The effect of discrete energy levels leads to oscillations in the rate of escape from the zero voltage state as a function of the bias current, observed at different temperatures. The oscillation spacing fits that expected from the energy level quantization.

Abstract We measured the transport properties and charge noise of superconducting single-electron... more Abstract We measured the transport properties and charge noise of superconducting single-electron transistors at the temperature of 0.3 K. The devices were fabricated with different ratios between charging and Josephson energies in order to explore their behavior in different experimental situations. We show that, in spite of the substantial thermal fluctuation, it is possible to extract from the data the values of the device parameters and information on the various tunneling mechanisms.

Abstract. Superconducting devices based on the Josephson effect are effectively used for the impl... more Abstract. Superconducting devices based on the Josephson effect are effectively used for the implementation of qubits and quantum gates. The manipulation of superconducting qubits is generally performed by using microwave pulses with frequencies from 5 to 15 GHz, obtaining a typical operating frequency from 100 MHz to 1 GHz. A manipulation based on simple pulses in the absence of microwaves is also possible.

Page 1. F. Chiarello1, P. Carelli2, MG Castellano1, C. Cosmelli3, R. Leoni1, F. Mattioli1, S. Pol... more Page 1. F. Chiarello1, P. Carelli2, MG Castellano1, C. Cosmelli3, R. Leoni1, F. Mattioli1, S. Poletto1, D. Simeone1, G. Torrioli1 1) INFN and Istituto di Fotonica e Nanotecnologie - CNR, via Cineto Romano 42, 00156 Roma 2) INFN andUniversità dell'Aquila, Monteluco di Roio, 67040 L'Aquila 3) INFN and Università di Roma “La Sapienza”, P.le A. Moro 2, 00185 Roma Superconducting Josephson Elements for Quantum Computing Page 2.

Abstract We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junction... more Abstract We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junctions made by a thin film of heavily doped silicon in contact with superconducting electrodes through Schottky barriers. Doped silicon films were chemical vapor deposited on silicon-on-insulator substrates and laterally dry etched in mesas. Aluminum or, alternatively, niobium contacts were deposited on the mesas.

Abstract We describe a simple and efficient scheme for the readout of a tunable flux qubit, and p... more Abstract We describe a simple and efficient scheme for the readout of a tunable flux qubit, and present preliminary experimental tests for the preparation, manipulation and final readout of the qubit state, performed in the incoherent regime at liquid helium temperature.

Abstract The flux states of a rf superconducting quantum interference device (SQUID) can be used ... more Abstract The flux states of a rf superconducting quantum interference device (SQUID) can be used to investigate macroscopic quantum effects, the most challenging of which is the detection of quantum coherent oscillations, and are promising candidates for the implementation of quantum computing. The use of a proper readout system is of utmost importance for these purposes.

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.

One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA a... more One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor thermometers. The pixels have metallic X-ray absorbers and are read-out by multiplexed SQUID electronics. The requirements for this instrument are demanding.

Abstract We introduce a three-junction superconducting quantum interference device (SQUID) that c... more Abstract We introduce a three-junction superconducting quantum interference device (SQUID) that can be used as an optimal tunable element in Josephson quantum computing applications. This device can replace the simple dc SQUID generally used as a tunable element in this kind of applications, with a series of advantages concerning the coherence time and the tolerance to small errors. We study the device both theoretically and experimentally at 4.2 K, obtaining a good agreement between the results.

We have investigated the pair tunneling process in step-edge Josephson junctions by studying the ... more We have investigated the pair tunneling process in step-edge Josephson junctions by studying the lifetime of the metastable zero-voltage state determined by the thermal activation out of the potential well. The junctions have a hysteretic current–voltage characteristic at 4.2 K, which allows the recording of transitions and switching distribution from the Josephson current to the resistive state. By applying an external magnetic field, we have found a strong dependence of the activation energy on the field intensity.

Abstract We present a methodology of network data analysis applied to the search for coincident b... more Abstract We present a methodology of network data analysis applied to the search for coincident burst excitations over a 24 h long data set collected by AURIGA, EXPLORER, NAUTILUS and Virgo detectors during September 2005. The search of candidate triggers was performed independently on each of the data sets from single detectors. We looked for two-fold time coincidences between these candidates using an algorithm optimized for a given population of sources

We report on experiments performed to probe quantum coherence in a system consisting of an rf-SQU... more We report on experiments performed to probe quantum coherence in a system consisting of an rf-SQUID in which the Josephson junction is replaced by a small loop containing two junctions in parallel. At temperatures of the order of 10 mK the system may develop three potential energy wells, which modify the usual two well energy profile and thereby verify the qubit manipulation strategy.

bicrystal dc-superconducting quantum interference devices (SQUIDs) and single layer magnetometers... more bicrystal dc-superconducting quantum interference devices (SQUIDs) and single layer magnetometers working at 77 K have been fabricated and analyzed. Samples have been made in situ by cylindrical magnetron dc sputtering on [001] bicrystal substrates. Magnetic flux noise levels and magnetic field sensitivities by standard flux-locked-loop electronics have been measured out on dc-SQUIDs and magnetometers, respectively.

Abstract We discuss and demonstrate a prototype of superconducting transformer with a flux transf... more Abstract We discuss and demonstrate a prototype of superconducting transformer with a flux transfer function that can be varied in a wide range, by acting on a control parameter.

Abstract The dc-superconducting quantum interference device (SQUID) is a low-noise converter from... more Abstract The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit of ħ/2. A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve.

Abstract We cooled down the electrons of a 3 μm 3 copper strip by using an on-chip electronic mic... more Abstract We cooled down the electrons of a 3 μm 3 copper strip by using an on-chip electronic microcooler made by a superconductor-insulator-normal-insulator-superconductor (SINIS) structure. We obtained an electron temperature drop ΔT≃-10 mK at a temperature of the bath slightly above T b= 500 mK and we estimated a cooling power slightly larger than 20 pW at this temperature. In contrast to previous experiments, we obtained this result operating with a simple 3 He refrigerator.

Abstract The data collected during 2005 by the resonant bar Explorer are divided into segments an... more Abstract The data collected during 2005 by the resonant bar Explorer are divided into segments and incoherently summed in order to perform an all-sky search for periodic gravitational wave signals. The parameter space of the search spanned about 40 Hz in frequency, over 23927 positions in the sky. Neither source orbital corrections nor spindown parameters have been included, with the result that the search was sensitive to isolated neutron stars with a frequency drift less than 6× 10− 11 Hz s− 1.

Abstract We present an experimental study on the retrapping process of a hysteretic, high-quality... more Abstract We present an experimental study on the retrapping process of a hysteretic, high-quality Josephson junction; namely, we have measured the distribution of the values at which the junction switches back from the voltage state to the zero-voltage state, as a function of the applied magnetic field. While the opposite process (escape from the zero-voltage state) has been extensively studied in the past, both from the theoretical and the experimental point of view, little is found in the literature on the retrapping process.

We present measurements of the supercurrent decay in high quality Nb/AlOx/Nb Josephson junctions ... more We present measurements of the supercurrent decay in high quality Nb/AlOx/Nb Josephson junctions which show evidence of energy-level quantization within the washboard potential describing the junction. The effect of discrete energy levels leads to oscillations in the rate of escape from the zero voltage state as a function of the bias current, observed at different temperatures. The oscillation spacing fits that expected from the energy level quantization.

Abstract We measured the transport properties and charge noise of superconducting single-electron... more Abstract We measured the transport properties and charge noise of superconducting single-electron transistors at the temperature of 0.3 K. The devices were fabricated with different ratios between charging and Josephson energies in order to explore their behavior in different experimental situations. We show that, in spite of the substantial thermal fluctuation, it is possible to extract from the data the values of the device parameters and information on the various tunneling mechanisms.

Abstract. Superconducting devices based on the Josephson effect are effectively used for the impl... more Abstract. Superconducting devices based on the Josephson effect are effectively used for the implementation of qubits and quantum gates. The manipulation of superconducting qubits is generally performed by using microwave pulses with frequencies from 5 to 15 GHz, obtaining a typical operating frequency from 100 MHz to 1 GHz. A manipulation based on simple pulses in the absence of microwaves is also possible.