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Spectroscopy of low-frequency noise and its temperature dependence in a superconducting qubit

Physical Review B 2012年第17期85卷 174521-174521页

作者： Fei Yan Jonas Bylander Simon Gustavsson Fumiki Yoshihara Khalil Harrabi David G. Cory Terry P. Orlando Yasunobu Nakamura Jaw-Shen Tsai William D. Oliver Department of Nuclear Science and Engineering Massachusetts Institute of Technology (MIT) Cambridge Massachusetts 02139 USA Research Laboratory of Electronics MIT Cambridge Massachusetts 02139 USA Institute of Physical and Chemical Research (RIKEN) Wako Saitama 351-0198 Japan Institute for Quantum Computing and Department of Chemistry University of Waterloo Ontario Canada N2L 3G1 Perimeter Institute for Theoretical Physics Waterloo Ontario Canada N2J 2W9 Department of Electrical Engineering and Computer Science MIT Cambridge Massachusetts 02139 USA Green Innovation Research Laboratories NEC Corporation Tsukuba Ibaraki 305-8501 Japan MIT Lincoln Laboratory 244 Wood Street Lexington Massachusetts 02420 USA

We report a direct measurement of the low-frequency noise spectrum in a superconducting flux qubit. Our method uses the noise sensitivity of a free-induction Ramsey interference experiment, comprising free evolution in the presence of noise for a fixed period of time followed by single-shot qubit-state measurement. Repeating this procedure enables Fourier-transform noise spectroscopy with access to frequencies up to the achievable repetition rate, a regime relevant to dephasing in ensemble-averaged time-domain measurements such as Ramsey interferometry. Rotating the qubit's quantization axis allows us to measure two types of noise: effective flux noise and effective critical-current or charge noise. For both noise sources, we observe that the very same 1/f-type power laws measured at considerably higher frequencies (0.2−20 MHz) are consistent with the noise in the 0.01−100-Hz range measured here. We find no evidence of temperature dependence of the noises over 65−200 mK, and also no evidence of time-domain correlations between the two noises. These methods and results are pertinent to the dephasing of all superconducting qubits.

关键词： QUBITS PHYSICS experiments SUPERCONDUCTORS FOURIER transform infrared spectroscopy TIME-domain analysis CORRELATION (Statistics) TEMPERATURE effect

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Experimental Realization of Decoherence-Free Subspace in Neutron Interferometry

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Physical Review Letters 2011年第15期107卷 150401-150401页

作者： D. A. Pushin M. G. Huber M. Arif D. G. Cory Department of Nuclear Science and Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA National Institute of Standards and Technology Gaithersburg Maryland 20899 USA Perimeter Institute for Theoretical Physics Waterloo Ontario Canada Institute for Quantum Computing and Department of Chemistry University of Waterloo Ontario Canada

A decoherence-free subspace (DFS) is an important class of quantum-error-correcting (QEC) codes that have been proposed for fault-tolerant quantum computation. The applications of QEC techniques, however, are not limited to quantum-information processing (QIP). Here we demonstrate how QEC codes may be used to improve experimental designs of quantum devices to achieve noise suppression. In particular, neutron interferometry is used as a test bed to show the potential for adding quantum error correction to quantum measurements. We built a five-blade neutron interferometer that incorporates both a standard Mach-Zender configuration and a configuration based on a DFS. Experiments verify that the DFS interferometer is protected against low-frequency mechanical vibrations. We anticipate these improvements will increase the range of applications for matter-wave interferometry.

关键词： INFORMATION processing INFORMATION science NOISE NEUTRONS -- Spectra NUCLEAR spectroscopy NEUTRON interferometry

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Squeezing-enhanced adaptive optical phase estimation

Squeezing-enhanced adaptive optical phase estimation

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quantum Electronics and Laser Science Conference

作者： Yonezawa, H. Nakane, D. Wheatley, T.A. Iwasawa, K. Takeda, S. Arao, H. Berry, D.W. Ralph, T.C. Wiseman, H.M. Huntington, E.H. Furusawa, A. Department of Applied Physics School of Engineering University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan Centre for Quantum Computer Technology Australian Research Council Australia School of Engineering and Information Technology University College University of New South Wales Canberra ACT 2600 Australia Institute for Quantum Computing University of Waterloo Waterloo ON N2L 3G1 Canada Department of Physics University of Queensland Brisbane QLD 4072 Australia Centre for Quantum Dynamics Griffith University Brisbane QLD 4111 Australia

We demonstrate squeezing-enhanced adaptive optical phase estimation for a stochastically varying phase. By using a continuous-wave phase squeezed beam, estimation accuracy is improved by a factor of 1.4 compared to a ... 详细信息

ISBN: (纸本)9781557529107

关键词： Acoustooptic modulators Coherent states Parametric oscillators Phase estimation Phase noise Squeezed states Squeezed states (270.6570) quantum information and processing (270.5585)

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Adaptive Optical Phase Estimation Using Time‐Symmetric quantum Smoothing

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AIP Conference Proceedings 2011年第1期1363卷 129-132页

作者： T. A. Wheatley D. W. Berry H. Yonezawa D. Nakane H. Arao D. T. Pope T. C. Ralph H. M. Wiseman A. Furusawa E. H. Huntington a Centre for Quantum Computer Technology Australian Research Council bSchool of Engineering and Information Technology The University of New South Wales Canberra 2600 ACT Australia cInstitute for Quantum Computing University of Waterloo Waterloo ON Canada dDepartment of Applied Physics and Quantum Phase Electronics Center School of Engineering The University of Tokyo 7‐3‐1 Hongo Bunkyo‐ku Tokyo 113‐8656 Japan ePerimeter Institute for Theoretical Physics 31 Caroline Street N Waterloo ONN2L3G1 Canada fDepartment of Physics Centre for Quantum Computing Technology University of Queensland Brisbane 4072 QLD Australia gCentre for Quantum Dynamics Centre for Quantum Computing Technology Griffith University Brisbane 4111 QLD Australia

We present an experimental demonstration of quantum smoothing, a non causal version of quantum parameter estimation that has applications from gravitational wave detection to quantum key distribution. An existing technique for this type of parameter estimation is quantum filtering, which uses past observations only. The technique presented here is time‐symmetric that uses past and future observations to obtain a more precise estimate. We couple this innovative estimation technique with an adaptive detection scheme to demonstrate an estimation of the optical phase of light measured to be 2.24 ± 0.14 times better than the standard quantum limit. This approaches our theoretically derived prediction of a mean square error improvement of 22 times over the standard quantum limit [1].

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Hyperfine Interaction Estimation in Nitrogen Vacancy Center in Diamond using Weak Values

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AIP Conference Proceedings 2011年第1期1363卷 177-180页

作者： Yutaka Shikano Sota Kagami Shu Tanaka Akio Hosoya aDepartment of Physics Tokyo Institute of Technology Meguro Tokyo 152‐8551 Japan bDepartment of Mechanical Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA cResearch Center for Quantum Computing Interdisciplinary Graduate School of Science and Engineering Kinki University Higashi Osaka Osaka 577‐8502 Japan

We propose a scheme to experimentally evaluate the hyperfine interaction between a nitrogen vacancy (NV) electron spin and a nearby 13C nuclear spin in the NV center in diamond. The advantages of our proposal are that the shorter time region is only used and the condition for evaluating the relative position between the spins can be removed.

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quantum Codes Give Counterexamples to the Unique Preimage Conjecture of the N-Representability Problem

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Physical Review Letters 2011年第11期106卷 110501-110501页

作者： Samuel A. Ocko Xie Chen Bei Zeng Beni Yoshida Zhengfeng Ji Mary Beth Ruskai Isaac L. Chuang Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts USA Department of Mathematics and Statistics University of Guelph Guelph Ontario Canada Institute for Quantum Computing University of Waterloo Waterloo Ontario Canada Perimeter Institute for Theoretical Physics Waterloo Ontario Canada Department of Electrical and Computer Engineering Tufts University Medford Massachusetts USA

It is well known that the ground state energy of many-particle Hamiltonians involving only 2-body interactions can be obtained using constrained optimizations over density matrices which arise from reducing an N-particle state. While determining which 2-particle density matrices are “N-representable” is a computationally hard problem, all known extreme N-representable 2-particle reduced density matrices arise from a unique N-particle preimage, satisfying a conjecture established in 1972. We present explicit counterexamples to this conjecture through giving Hamiltonians with 2-body interactions which have degenerate ground states that cannot be distinguished by any 2-body operator. We relate the existence of such counterexamples to quantum error correction codes and topologically ordered spin systems.

关键词： Hamiltonians

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Behind the quantum and size effects: Broken-bond-induced local strain and skin-depth densified quantum trapping of charge and energy

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Key engineering Materials 2010年 444卷 17-45页

作者： Pan, Likun Gu, Mingxia Ouyang, Gang Sun, Chang Q. Engineering Research Center for Nanophotonics and Advanced Instrument Department of Physics East China Normal University Shanghai 200062 China Institute of High Performance Computing ASTAR 1 Fusionopolis Way Singapore 138632 Singapore School of Electrical and Electronic Engineering Nanyang Technological University Singapore 639798 Singapore Key Laborastory of Low-dimensional Materials and Application Technolgies Institute of Quantum Enginering and Moicro-Nano Energy Technology Xiangtan University Changsha 411105 China

ISBN: (纸本)9780878492657

Shrinking the size of a solid down to nanometer scale is indeed fascinating, which makes all the otherwise constant physical quantities to be tunable such as the Young's modulus, dielectric constant, melting point, etc. The variation of size also generates novel properties that can hardly be seen in the bulk such as the conductor-insulator and nonmagnetic-magnetic transition of noble metals at the nanoscale. Although the physics of materials at the nanoscale has been extensively investigated, the laws governing the energetic and dynamic behavior of electrons at such a scale and their consequences on the tunable physical properties of nanostructures have not been well understood [C. Q. Sun, Prog Solid State Chem 35, 1-159 (2007);Prog Mater Sci 54, 179-307 (2009)]. The objective of the contribution is to update the recent progress in dealing with the coordination-resolved energetic and dynamic behavior of bonds in the low-dimensional systems with consideration of the joint effect of temperature and pressure. It is shown that the broken-bond-induced local strain and the associated charge and energy quantum trapping at the defect sites perturbs the atomic cohesive energy, electroaffinity, the Hamiltonian and the associated properties of entities ranging from point defects, surfaces, nanocavities and nanostructures. Application of the theories to observations has led to consistent understanding of the behavior of nanometer-sized materials and the interdependence of these entities as well as the means of determining the bond energy through the temperature-dependent measurements. © (2010) Trans Tech Publications.

关键词： Hamiltonians

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Adaptive optical phase estimation

Adaptive optical phase estimation

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Conference on Lasers and Electro-Optics

作者： Nakane, D. Wheatley, T.A. Berry, D.W. Yonezawa, H. Arao, H. Pope, D.T. Ralph, T.C. Wiseman, H.M. Huntington, E.H. Furusawa, A. Department of Applied Physics School of Engineering University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo Japan Centre for Quantum Computer Technology Australian Research Council Australia School of Engineering and Information Technology University College University of New South Wales Canberra 2600 ACT Australia Institute for Quantum Computing University of Waterloo Waterloo N2L 3G1 ON Canada Perimeter Institute Waterloo ON Canada Department of Physics University of Queensland Brisbane 4072 QLD Australia Centre for Quantum Dynamics Griffith University Brisbane 4111 QLD Australia

We experimentally performed adaptive phase estimation using time-symmetric quantum smoothing for a stochastically varying phase on continuous wave coherent beam. We demonstrate better accuracy than conventional method... 详细信息

ISBN: (纸本)9781557528902

关键词： Linear filtering Modulators Phase estimation Ti:sapphire lasers Titanium lasers Instrumentation, measurement, and metrology (120.0120) Phase measurement (120.5050) Adaptive interferometry (120.1088)

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Dimensional evolution of spin correlations in the magnetic pyrochlore Yb2Ti2O7

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Physical Review B 2011年第17期84卷 174442-174442页

作者： K. A. Ross L. R. Yaraskavitch M. Laver J. S. Gardner J. A. Quilliam S. Meng J. B. Kycia D. K. Singh Th. Proffen H. A. Dabkowska B. D. Gaulin Department of Physics and Astronomy McMaster University Hamilton Ontario L8S 4M1 Canada Department of Physics and Astronomy and Guelph-Waterloo Physics Institute University of Waterloo Waterloo ON N2L 3G1 Canada Institute for Quantum Computing University of Waterloo Waterloo ON N2L 3G1 Canada Materials Research Division Risö DTU Technical University of Denmark DK-4000 Roskilde Denmark Nano-Science Center Niels Bohr Institute University of Copenhagen DK-2100 Köbenhavn Denmark Laboratory for Neutron Scattering Paul Scherrer Institut 5232 Villigen PSI Switzerland Indiana University 2401 Milo B. Sampson Lane Bloomington Indiana 47408 USA National Institute of Standards and Technology 100 Bureau Drive MS 6102 Gaithersburg Maryland 20899-6102 USA Dept. of Materials Science and Engineering University of Maryland College Park Maryland 20742 Los Alamos National Laboratory Los Alamos New Mexico 87545 USA Spallation Neutron Source Experimental Facilities Division Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge Tennessee 37831 USA Brockhouse Institute for Materials Research McMaster University Hamilton Ontario L8S 4M1 Canada Canadian Institute for Advanced Research 180 Dundas St. W. Toronto Ontario M5G 1Z8 Canada

The pyrochlore material Yb2Ti2O7 displays unexpected quasi-two-dimensional (2D) magnetic correlations within a cubic lattice environment at low temperatures, before entering an exotic disordered ground state below T=265 mK. We report neutron scattering measurements of the thermal evolution of the 2D spin correlations in space and time. Short-range three-dimensional (3D) spin correlations develop below 400 mK, accompanied by a suppression in the quasielastic (QE) scattering below ∼0.2 meV. These show a slowly fluctuating ground state with spins correlated over short distances within a kagome-triangular-kagome (KTK) stack along [111], which evolves to isolated kagome spin stars at higher temperatures. Furthermore, low-temperature specific heat results indicate a sample dependence to the putative transition temperature that is bounded by 265 mK, which we discuss in the context of recent mean field theoretical analysis.

关键词： YTTERBIUM TITANATES PYROCHLORE QUASIELASTIC neutron scattering MEAN field theory

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quantum State Reduction for Universal Measurement Based Computation

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Physical Review Letters 2010年第2期105卷 020502-020502页

作者： Xie Chen Runyao Duan Zhengfeng Ji Bei Zeng Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts USA Centre for Quantum Computation and Intelligent Systems (QCIS) Faculty of Engineering and Information Technology University of Technology Sydney NSW Australia Department of Computer Science and Technology Tsinghua National Laboratory for Information Science and Technology Tsinghua University Beijing China Perimeter Institute for Theoretical Physics Waterloo Ontario Canada State Key Laboratory of Computer Science Institute of Software Chinese Academy of Sciences Beijing China Institute for Quantum Computing University of Waterloo Waterloo Ontario Canada Department of Combinatorics and Optimization University of Waterloo Waterloo Ontario Canada

Measurement based quantum computation, which requires only single particle measurements on a universal resource state to achieve the full power of quantum computing, has been recognized as one of the most promising models for the physical realization of quantum computers. Despite considerable progress in the past decade, it remains a great challenge to search for new universal resource states with naturally occurring Hamiltonians and to better understand the entanglement structure of these kinds of states. Here we show that most of the resource states currently known can be reduced to the cluster state, the first known universal resource state, via adaptive local measurements at a constant cost. This new quantum state reduction scheme provides simpler proofs of universality of resource states and opens up plenty of space to the search of new resource states.

关键词： quantum computers

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