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Experimental Implementation of Encoded Logical Qubit Operations in a Perfect Quantum Error Correcting Code

Physical Review Letters 2012年第10期109卷 100503-100503页

作者： Jingfu Zhang Raymond Laflamme Dieter Suter Fakultät Physik Technische Universität Dortmund D-44221 Dortmund Germany Institute for Quantum Computing and Department of Physics University of Waterloo Waterloo Ontario N2L 3G1 Canada Perimeter Institute for Theoretical Physics Waterloo Ontario N2J 2W9 Canada

Large-scale universal quantum computing requires the implementation of quantum error correction (QEC). While the implementation of QEC has already been demonstrated for quantum memories, reliable quantum computing requires also the application of nontrivial logical gate operations to the encoded qubits. Here, we present examples of such operations by implementing, in addition to the identity operation, the NOT and the Hadamard gate to a logical qubit encoded in a five qubit system that allows correction of arbitrary single-qubit errors. We perform quantum process tomography of the encoded gate operations, demonstrate the successful correction of all possible single-qubit errors, and measure the fidelity of the encoded logical gate operations.

关键词： gate array circuits QUBITS QUANTUM error correcting codes QUANTUM theory GEOMETRIC tomography ERROR analysis (Mathematics)

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Image processing with cellular nonlinear networks implemented on field-programmable gate arrays for real-time applications in nuclear fusion

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REVIEW OF SCIENTIFIC INSTRUMENTS 2010年第8期81卷 083505-083505页

作者： Palazzo, S. Murari, A. Vagliasindi, G. Arena, P. Mazon, D. De Maack, A. Univ Catania Dipartimento Ingn Elettr Elettron & Sistemi I-95125 Catania Italy EURATOM ENEA Fus Consorzio RFX Assoc I-35127 Padua Italy CEA Cadarache Assoc EURATOM CEA F-13108 St Paul Les Durance France ENSAM Arts & Met Paris Tech Engn Coll F-13100 Paris Aix En Provence France JET EFDA Culham Sci Ctr Abingdon OX14 3DB Oxon England

In the past years cameras have become increasingly common tools in scientific applications. They are now quite systematically used in magnetic confinement fusion, to the point that infrared imaging is starting to be used systematically for real-time machine protection in major devices. However, in order to guarantee that the control system can always react rapidly in case of critical situations, the time required for the processing of the images must be as predictable as possible. The approach described in this paper combines the new computational paradigm of cellular nonlinear networks (CNNs) with field-programmable gate arrays and has been tested in an application for the detection of hot spots on the plasma facing components in JET. The developed system is able to perform real-time hot spot recognition, by processing the image stream captured by JET wide angle infrared camera, with the guarantee that computational time is constant and deterministic. The statistical results obtained from a quite extensive set of examples show that this solution approximates very well an ad hoc serial software algorithm, with no false or missed alarms and an almost perfect overlapping of alarm intervals. The computational time can be reduced to a millisecond time scale for 8 bit 496 x 560-sized images. Moreover, in our implementation, the computational time, besides being deterministic, is practically independent of the number of iterations performed by the CNN-unlike software CNN implementations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3477994]

关键词： CAMERAS INFRARED imaging FUSION (Phase transformation) COMPUTER software industry gate array circuits

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Quantum Coherence Engineering in the Integer Quantum Hall Regime

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Physical Review Letters 2012年第25期108卷 256802-256802页

作者： P-A. Huynh F. Portier H. le Sueur G. Faini U. Gennser D. Mailly F. Pierre W. Wegscheider P. Roche CEA SPEC Nanoelectronics Group URA 2464 F-91191 Gif-sur-Yvette France CNRS LPN Phynano Team route de Nozay 91460 Marcoussis France Laboratory for Solid State Physics ETH Zürich CH-8093 Zürich Switzerland

We present an experiment where the quantum coherence in the edge states of the integer quantum Hall regime is tuned with a decoupling gate. The coherence length is determined by measuring the visibility of quantum interferences in a Mach-Zehnder interferometer as a function of temperature, in the quantum Hall regime at a filling factor 2. The temperature dependence of the coherence length can be varied by a factor of 2. The strengthening of the phase coherence at finite temperature is shown to arise from a reduction of the coupling between copropagating edge states. This opens the way for a strong improvement of the phase coherence of quantum Hall systems. The decoupling gate also allows us to investigate how interedge state coupling influences the quantum interferences’ dependence on the injection bias. We find that the finite bias visibility can be decomposed into two contributions: a Gaussian envelope which is surprisingly insensitive to the coupling, and a beating component which, on the contrary, is strongly affected by the coupling.

关键词： QUANTUM theory COHERENT states QUANTUM Hall effect PHYSICS experiments gate array circuits INTERFEROMETERS QUANTUM interference GAUSSIAN processes

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Designer Spin Pseudomolecule Implemented with Trapped Ions in a Magnetic Gradient

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Physical Review Letters 2012年第22期108卷 220502-220502页

作者： A. Khromova Ch. Piltz B. Scharfenberger T. F. Gloger M. Johanning A. F. Varón Ch. Wunderlich Department Physik Naturwissenschaftlich-Technische Fakultät Universität Siegen 57068 Siegen Germany

We report on the experimental investigation of an individual pseudomolecule using trapped ions with adjustable magnetically induced J-type coupling between spin states. Resonances of individual spins are well separated and are addressed with high fidelity. Quantum gates are carried out using microwave radiation in the presence of thermal excitation of the pseudomolecule’s vibrations. Demonstrating controlled-NOT gates between non-nearest neighbors serves as a proof-of-principle of a quantum bus employing a spin chain. Combining advantageous features of nuclear magnetic resonance experiments and trapped ions, respectively, opens up a new avenue toward scalable quantum information processing.

关键词： ION traps QUANTUM theory NUCLEAR spin MAGNETIC materials MICROWAVES gate array circuits THERMAL analysis

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gate-Controlled Spin Injection at LaAlO3/SrTiO3 Interfaces

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Physical Review Letters 2012年第18期108卷 186802-186802页

作者： N. Reyren M. Bibes E. Lesne J.-M. George C. Deranlot S. Collin A. Barthélémy H. Jaffrès Unité Mixte de Physique CNRS-Thales 1 Av. A. Fresnel 91767 Palaiseau France and Université Paris-Sud 91405 Orsay France

We report results of electrical spin injection at the high-mobility quasi-two-dimensional electron system (2-DES) that forms at the LaAlO3/SrTiO3 interface. In a nonlocal, three-terminal measurement geometry, we analyze the voltage variation associated with the precession of the injected spin accumulation driven by perpendicular or transverse magnetic fields (Hanle and inverted Hanle effect). The influence of bias and back-gate voltages reveals that the spin accumulation signal is amplified by resonant tunneling through localized states in the LaAlO3 strongly coupled to the 2-DES by tunneling transfer.

关键词： gate array circuits NUCLEAR spin PLASMA injection LANTHANUM compounds TITANATES INTERFACES (Physical sciences) MAGNETIC fields

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Speed limits for quantum gates in multiqubit systems

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Physical Review A 2012年第5期85卷 052327-052327页

作者： S. Ashhab P. C. de Groot Franco Nori Advanced Science Institute RIKEN Wako-shi Saitama 351-0198 Japan Physics Department The University of Michigan Ann Arbor Michigan 48109-1040 USA Kavli Institute of Nanoscience Delft University of Technology P.O. Box 5046 2600 GA Delft The Netherlands

We use analytical and numerical calculations to obtain speed limits for various unitary quantum operations in multiqubit systems under typical experimental conditions. The operations that we consider include single-, two-, and three-qubit gates, as well as quantum-state transfer in a chain of qubits. We find in particular that simple methods for implementing two-qubit gates generally provide the fastest possible implementations of these gates. We also find that the three-qubit Toffoli gate time varies greatly depending on the type of interactions and the system's geometry, taking only slightly longer than a two-qubit controlled-not (cnot) gate for a triangle geometry. The speed limit for quantum-state transfer across a qubit chain is set by the maximum spin-wave speed in the chain.

关键词： QUANTUM theory SPEED limits gate array circuits QUBITS NUMERICAL analysis SPIN waves

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High-performance pentacene OTFT by incorporating Ti in LaON gate dielectric

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APPLIED PHYSICS LETTERS 2017年第2期111卷 023501-023501页

作者： Ma, Y. X. Han, C. Y. Tang, W. M. Lai, P. T. Univ Hong Kong Dept Elect & Elect Engn Pokfulam Rd Hong Kong Isl 999077 Hong Kong Peoples R China Xi An Jiao Tong Univ Sch Microelect Xian 710049 Peoples R China Hong Kong Polytech Univ Dept Appl Phys Hong Kong 999077 Hong Kong Peoples R China

Pentacene organic thin-film transistors (OTFT) using high-k LaTiON gate dielectric with different Ti contents are investigated. The LaxTi(1-x)ON films (with x = 1, 0.87, 0.76, and 0.67) are deposited by reactive sputtering followed by an annealing in N-2 at 200 degrees C. The OTFT with La0.87Ti0.13ON can achieve a high carrier mobility of 2.6 cm(2)/V.s, a small threshold voltage of -1.5 V, a small sub-threshold swing of 0.07 V/dec, and a small hysteresis of 0.17 V. AFM and X-ray photoelectron spectroscopy reveal that Ti can suppress the hygroscopicity of La oxide to achieve a smoother dielectric surface, which can result in larger pentacene grains and thus higher carrier mobility. All the devices show a clockwise hysteresis because both the LaOH formation and Ti incorporation can generate acceptor-like traps in the gate dielectric. Published by AIP Publishing.

关键词： PERFORMANCE of thin film transistors PENTACENE gate array circuits DIELECTRICS LANTHANUM compounds

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Towards Practical Classical Processing for the Surface Code

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Physical Review Letters 2012年第18期108卷 180501-180501页

作者： Austin G. Fowler Adam C. Whiteside Lloyd C. L. Hollenberg Centre for Quantum Computation and Communication Technology School of Physics The University of Melbourne Victoria 3010 Australia

The surface code is unarguably the leading quantum error correction code for 2D nearest neighbor architectures, featuring a high threshold error rate of approximately 1%, low overhead implementations of the entire Clifford group, and flexible, arbitrarily long-range logical gates. These highly desirable features come at the cost of significant classical processing complexity. We show how to perform the processing associated with an n×n lattice of qubits, each being manipulated in a realistic, fault-tolerant manner, in O(n2) average time per round of error correction. We also describe how to parallelize the algorithm to achieve O(1) average processing per round, using only constant computing resources per unit area and local communication. Both of these complexities are optimal.

关键词： ERROR-correcting codes (Information theory) QUANTUM communication NEAREST neighbor analysis (Statistics) gate array circuits GROUP theory COMPUTATIONAL complexity

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Synthesis of arbitrary SU(3) transformations of atomic qutrits

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Physical Review A 2012年第3期85卷 032331-032331页

作者： Nikolay V. Vitanov Department of Physics Sofia University 5 James Bourchier blvd. 1164 Sofia Bulgaria

Several scenarios are proposed and analyzed for engineering of arbitrary preselected SU(3) transformations of laser-driven atomic qutrits. Two of the most natural implementations of qutrits are considered, in which the three qutrit states are coupled to each other via two-photon transitions through either (i) a common state in a tripod linkage pattern or (ii) two upper states in an M-shaped linkage chain. The SU(3) transformation for the tripod qutrit can be realized by 3 Givens SU(2) rotations, which require 9 consecutive interaction steps. Alternatively, because under certain conditions the propagator of the tripod system reduces to the Householder reflection operator, any SU(3) transformation can be constructed physically by 3 Householder reflections, each of which is implemented in a single interaction step. As an example, the discrete Fourier transform can be synthesized by 7 consecutive interaction steps with Givens rotations or, alternatively, by only a single Householder reflection and a phase gate. For the M-qutrit, the propagator is given by coupled Householder reflections and it cannot be reduced to Givens rotations or independent Householder reflections. By using these coupled Householder reflections it is shown that an arbitrary SU(3) transformation of the M qutrit can be realized with just two fields in at most 3 interaction steps; the discrete Fourier transform, in particular, requires only 2 interaction steps.

关键词： SUPERSYMMETRY (Physics) TRANSFORMATIONS (Mathematics) ATOMIC theory ENERGY levels (Quantum mechanics) gate array circuits QUANTUM communication

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Method for preparing two-atom entangled states in circuit QED and probing it via quantum nondemolition measurements

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Physical Review A 2013年第4期88卷 042324-042324页

作者： D. Z. Rossatto C. J. Villas-Boas Departamento de Física Universidade Federal de São Carlos CEP 13565-905 São Carlos SP Brazil

We propose a probabilistic scheme to prepare a maximally entangled state between a pair of two-level atoms coupled to a leaking cavity mode in circuit QED, without requiring precise time control of the system evolution and initial atomic state. We show that the steady state of this dissipative system is a mixture of two parts, where the atoms are either in their ground state or in a maximally entangled one. Then, by applying a weak probe field to the cavity mode, we are able to discriminate those states without disturbing the atomic system, i.e., to perform a quantum nondemolition measurement via the cavity transmission. In this scheme, one has maximum cavity transmission only when the atomic system is in an entangled state, so that a single click in the detector is enough to be sure that the atoms are in a maximally entangled state. Our scheme relies on an interference effect as it happens in an electromagnetically induced transparency phenomenon so that it works even in the limit of a cavity decay rate much stronger than the atom-field coupling.

关键词： QUANTUM entanglement QUANTUM electrodynamics QUANTUM gates gate array circuits ENERGY dissipation ELECTROMAGNETISM

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