Emilio Sciacca

Aspects of Qubit Dynamics in the Presence of Leakage

Nano-electronics devices such as small-capacitance Josephsonjunction circuits appear to be promising systems to implementquantum logic. While the elementary unit of a quantum computeris a two-state system (the qubit) the computational space of aJosephson junction qubit is a subset of a larger Hilbertspace. Therefore quantum leakage may occur, i.e. during theoperation of the device the quantum state may escape partiallyfrom the computational subspace. We study the consequences ofleakage for the fidelity of Josephson qubits and discuss howthe gate design can be optimized.

Single Photon Avalanche Diodes: Towards the Large Bidimensional Arrays

Single photon detection is one of the most challenging goals of photonics. In recent years, the study of ultra-fast and/or low-intensity phenomena has received renewed attention from the academic and industrial communities. Intense research activity has been focused on bio-imaging applications, bio-luminescence, bio-scattering methods, and, more in general, on several applications requiring high speed operation and high timing resolution. In this paper we present design and characterization of bi-dimensional arrays of a next generation of single photon avalanche diodes (SPADs). Single photon sensitivity, dark noise, afterpulsing and timing resolution of the single SPAD have been examined in several experimental conditions. Moreover, the effects arising from their integration and the readout mode have also been deeply investigated.

A New Generation of SPAD—Single-Photon Avalanche Diodes

Design and characterization of a new generation of single-photon avalanche diodes (SPAD) array, manufactured by ST-Microelectronics in Catania, Italy, are presented. Device performances, investigated in several experimental conditions and here reported, demonstrate their suitability in many applications. SPADs are thin p-n junctions operating above the breakdown condition in Geiger mode at low voltage. In this regime a single charged carrier injected into the depleted layer can trigger a self-sustaining avalanche, originating a detectable signal. Dark counting rate at room temperature is down to 10 s-1 for devices with an active area of 10 mum in diameter, and 103 s-1 for those 50 mum wide. SPAD quantum efficiency, measured in the range 350-1050 nm, can be comparable to that of a typical silicon based detector and reaches the values of about 50% at 550 nm. Finally, the low production costs and the integration possibility are other favorable features in sight of highly dense integrated 1-D or 2-D arrays.

Measurement of the hot carrier damage profile in LDMOS devices stressed at high drain voltage.

In this paper, the hot carrier degradation of laterally diffused nMOSFETs is investigated in detail by the analysis of the fundamental device parameters and charge pumping measurements. Starting from this experimental characterization a new approach based on charge pumping technique is developed to estimate the spatial distribution of the hot carrier damage. This methodology has been applied on test structures, obtaining good results in the prediction of both the interface states and the trapped charges profiling. The supporting assumptions have been verified by fitting to the electrical data and by means of a two-dimensional device simulation.

Characterization of SPAD Arrays: First Results

SPAD detectors are very promising for astrophysical applications. Large arrays are crucial to cover as much of the focal plane as possible. STMicroelectronics has developed various monolithic arrays of SPAD. At present, the manufacturing of 5×5 arrays (each with an active area of 40 μm and pitch between adjacent pixels of 240 μm) is completed and improvements in terms of pixels and technology are under study and development. An appropriate cryogenic system to host the packaged SPAD arrays and detection electronics to drive them have been designed and realized. Electro-optical characteristics of various arrays in different operating conditions have been measured and the obtained results are presented herein.

Silicon planar technology for single-photon optical detectors

In this paper we report the results relative to the design and fabrication of Single Photon Avalanche Detectors (SPAD) operating at low voltage in planar technology. These silicon sensors consist of pn junctions that are able to remain quiescent above the breakdown voltage until a photon is absorbed in the depletion volume. This event is detected through an avalanche current pulse. Device design and critical issues in the technology are discussed. Experimental test procedures are then described for dark-counting rate, afterpulsing probability, photon timing resolution, quantum detection efficiency. Through these experimental setups we have measured the electrical and optical performances of different SPAD technology generations. The results from these measurements indicate that in order to obtain low-noise detectors it is necessary to introduce a local gettering process and to realize the diode cathode through in situ doped polysilicon deposition. With such technology low noise detectors with dark counting rates at room temperature down to 10c/s for devices with 10mm diameter, down to 1kc/s for 50mm diameter have been obtained. Noticeable results have been obtained also as far as time jitter and quantum detection efficiency are concerned. This technology is suitable for monolithic integration of SPAD detectors and associated circuits. Small arrays have already been designed and fabricated. Preliminary results indicate that good dark count rate uniformity over the different array pixels has already been obtained.

Preliminary Test Measurements of the SPAD Array

This is a progress report on preliminary test measurements aimed to evaluate the performance of new Single Photon Avalanche Diodes (SPAD) developed by ST Microelectronics. Various samples with different dimensions (from 10 to 100 μm diameter) and two 5x5 arrays (20 and 40 μm) are manufactured by STM; some of which have been characterized. A brief description of the device and its main characteristics (dark, quantum efficiency and linearity) are presented.

Silicon p–n junctions biased above breakdown used as monitors of carrier lifetime

In this paper we show that single-photon avalanche detectors (SPADs) may have a strong potential as very sensitive on-wafer tools for lifetime monitoring, given their simple fabrication process and their straightforward use in the measurements. We have fabricated Si SPADs with n + -p structures and we show that dark counting has a simple exponential dependence on time, thus making it possible to extract a single lifetime parameter.

Correction to "Silicon planar technology for single-photon optical detectors"

Design and fabrication of single photon avalanche detector (SPAD) in planar technology is reported. Device design and critical issues in the technology are discussed. Experimental test procedures are described for dark-counting rate, afterpulsing probability, photon timing resolution, and quantum detection efficiency. Low-noise detectors are obtained, with dark counting rates down to 10 c/s for devices with 10 m diameter, down to 1 kc/s for 50 m diameter. The technology is suitable for monolithic integration of SPAD detectors and associated circuits.

Leakage and fidelity of real qubits

Abstract We analayze the class of error which is due to the fact that the qubit Hilbert space is actually a subspace of a larger Hilbert space. We study the fidelity and the leakage for one and two qubits operation and discuss, as a specific case, the recently proposed implementation with Josephson junctions. We also discuss possible ways of optimizing the operations against leakage.