Quantum Chaos Border for Quantum Computing

We study a generic model of quantum computer, composed of many qubits coupled by short-range interaction. Above a critical interqubit coupling strength, quantum chaos sets in, leading to quantum ergodicity of the computer eigenstates. In this regime the noninteracting qubit structure disappears, the eigenstates become complex and the operability of the computer is destroyed. Despite the fact that the spacing between multi-qubit states drops exponentially with the number of qubits $n$, we show that the quantum chaos border decreases only linearly with $n$. This opens a broad parameter region where the efficient operation of a quantum computer remains possible.Comment: revtex, 4 pages, 5 figures, more details and data adde

Resonant tunneling through ultrasmall quantum dots: zero-bias anomalies, magnetic field dependence, and boson-assisted transport

We study resonant tunneling through a single-level quantum dot in the presence of strong Coulomb repulsion beyond the perturbative regime. The level is either spin-degenerate or can be split by a magnetic field. We, furthermore, discuss the influence of a bosonic environment. Using a real-time diagrammatic formulation we calculate transition rates, the spectral density and the nonlinear $I-V$ characteristic. The spectral density shows a multiplet of Kondo peaks split by the transport voltage and the boson frequencies, and shifted by the magnetic field. This leads to zero-bias anomalies in the differential conductance, which agree well with recent experimental results for the electron transport through single-charge traps. Furthermore, we predict that the sign of the zero-bias anomaly depends on the level position relative to the Fermi level of the leads.Comment: 27 pages, latex, 21 figures, submitted to Phys. Rev.

Measurements of the Proton and Helium Spectra from CREAM-V

International audienceThe Cosmic Rays Energy And Mass (CREAM) balloon payload directly measures the composition and elemental spectra of cosmic rays in the upper stratosphere. It is designed to probe the acceleration mechanism and propagation history of cosmic rays at energies from 10$^{12}$ up to 10$^{15}$ eV. Being the fifth flight in a series of seven, CREAM-V took data above Antarctica for 39 days from December 1$^{st}$ 2009 to January 8$^{th}$ 2010. The instrument comprises a tungsten/scintillating fiber calorimeter using graphite as a target for the energy measurement which had been calibrated at CERN (European Organization for Nuclear Research). The charge measurement of the incident particles is performed by means of a Silicon Charge Detector (SCD), a Cherenkov Detector, a Cherenkov Camera (Cher-Cam) and a Timing Charge Detector (TCD). In this paper we present results from the on-going data analysis and compare them to data collected by the previous CREAM_III flight

Performance of the BACCUS Transition Radiation Detector

International audienceThe Boron And Carbon Cosmic rays in the Upper Stratosphere (BACCUS) balloon-borne exper-iment flew for 30 days over Antarctica in December 2016. It is the successor of the CREAMballoon program in Antarctica which recorded a total cumulative exposure of 161 days. BAC-CUS is primarily aimed to measure cosmic-ray boron and carbon fluxes at the highest energiesreachable with a balloon or satellite experiment, in order to provide essential information for abetter understanding of cosmic-ray propagation in the Galaxy. The payload is made of multipleparticle physics detectors which measure the charge up to Z=26 and energy of incident particlesfrom a few hundred GeV to a few PeV. The newly designed Transition Radiation Detector (TRD)measures signals that are a function of the charge and Lorentz factor. In April 2016, BACCUSwas taken to CERN in its flight configuration to characterize its detectors’ response to beams ofelectrons and pions. The performance of the TRD using beam test data are reported in this paper

Cosmic-ray Heavy Nuclei Spectra Using the ISS-CREAM Instrument

International audienceCosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) was designed to study high-energy cosmic rays up to PeV and recorded data from August 22nd, 2017 to February 12th, 2019 on the ISS. In this analysis, the Silicon Charge Detector (SCD), CALorimeter (CAL), and Top and Bottom Counting Detectors (TCD/BCD) are used. The SCD is composed of four layers and provides the measurement of cosmic-ray charges with a resolution of $\sim$0.2e. The CAL comprises 20 interleaved tungsten plates and scintillators, measures the incident cosmic-ray particles' energies, and provides a high energy trigger. The TCD/BCDs consist of photodiode arrays and plastic scintillators and provide a low-energy trigger. In this analysis, the SCD top layer is used for charge determination. Here, we present the heavy nuclei analysis using the ISS-CREAM instrument

e/p Separation Study Using the ISS-CREAM Top and Bottom Counting Detectors

International audienceCosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) is an experiment for studying the origin, acceleration, and propagation mechanisms of high-energy cosmic rays. The ISS-CREAM instrument was launched on the 14th of August 2017 to the ISS aboard the SpaceX-12 Dragon spacecraft. The Top and Bottom Counting Detectors (TCD/BCD) are parts of the ISS-CREAM instrument and designed for studying electron and gamma-ray physics. The TCD/BCD each consist of an array of 20 × 20 photodiodes on a plastic scintillator. The TCD/BCD can separate electrons from protons by using the difference between the shapes of electromagnetic and hadronic showers in the high energy region. The Boosted Decision Tree (BDT) method, which is a deep learning method, is used in this separation study. We will present results of the electron/proton separation study and rejection power in various energy ranges

The ISS-CREAM Silicon Charge Detector for identification of the charge of cosmic rays up to Z = 26: Design, fabrication and ground-test performance

International audienceThe Cosmic Ray Energetics And Mass experiment for the International Space Station (ISS-CREAM) is a space-borne mission designed for the precision measurement of the energy and elemental composition of cosmic rays. The Silicon Charge Detector (SCD), placed at the top of the ISS-CREAM payload, consists of 4 layers. Each layer has 2688 silicon pixels and associated electronics arranged in such a fashion that its active detection area of 78.2  ×  73.6 cm 2 is free of dead area. The foremost goal of the SCD is to efficiently and precisely measure the charge of cosmic rays passing through it. The 4-layer configuration was chosen to achieve the best precision in measuring the charge of cosmic rays within the constraints on the mass, volume and power allotted to it. The amount of material used for its support structure was minimized as well to reduce the chance of interactions of the cosmic ray within the structure. Given the placement of the SCD, its 4-layer configuration and the minimal amount of material in the cosmic-ray trajectory, the SCD is designed to measure the charge of cosmic rays ranging from protons to iron nuclei with excellent detection efficiency and charge resolution. We present the design and fabrication of the SCD as well as its performance during space environment tests which it underwent successfully. We also present its performance in charge measurement using heavy ions in a beam test at CERN, the European Organization for Nuclear Research

Measurement of High-energy Cosmic-Ray Proton Spectrum from the ISS-CREAM Experiment

International audienceThe Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) experiment successfully recorded data for 539 days from 2017 August to 2019 February. We report the energy spectrum of cosmic-ray protons from the ISS-CREAM experiment at energies from 1.60 × 10$^{3}$ to 6.55 × 10$^{5}$ GeV. The measured spectrum deviates from a single power law. A smoothly broken power-law fit to the data, including statistical and systematic uncertainties, shows the spectral index change at 9.0 × 10$^{3}$ GeV from 2.57 ± 0.03 to 2.82 ± 0.02 with a significance of greater than 3σ. This bump-like structure is consistent with a spectral softening recently reported by the balloon-borne CREAM, DAMPE, and NUCLEON, but ISS-CREAM extends measurements to higher energies