Communication in quantum networks of logical bus topology
T. Brougham, G. M. Nikolopoulos, and I. Jex
Perfect state transfer (PST) is discussed in the context of passive quantum networks with logical bus topology, where many logical nodes communicate using the same shared media without any external control. The conditions under which a number of point-to-point PST links may serve as building blocks ... [Phys. Rev. A 80, 052325 (2009)] published Thu Nov 19, 2009.
Quantum nondemolition measurements of a qubit coupled to a harmonic oscillator
Luca Chirolli and Guido Burkard
We theoretically describe the weak measurement of a two-level system (qubit) and quantify the degree to which such a qubit measurement has a quantum nondemolition (QND) character. The qubit is coupled to a harmonic oscillator, which undergoes a projective measurement. Information on the qubit state ... [Phys. Rev. B 80, 184509 (2009)] published Wed Nov 18, 2009.
Phonon-induced dephasing of singlet-triplet superpositions in double quantum dots without spin-orbit coupling
K. Roszak and P. Machnikowski
We show that singlet-triplet superpositions of two-electron spin states in a double quantum dot undergo a phonon-induced pure dephasing which relies only on the tunnel coupling between the dots and on the Pauli-exclusion principle. As such, this dephasing process is independent of spin-orbit couplin ... [Phys. Rev. B 80, 195315 (2009)] published Tue Nov 17, 2009.
NMR multiple quantum coherences in quasi-one-dimensional spin systems: Comparison with ideal spin-chain dynamics
Wenxian Zhang, Paola Cappellaro, Natania Antler, Brian Pepper, David G. Cory et al.
The F spins in a crystal of fluorapatite have often been used to experimentally approximate a one-dimensional spin system. Under suitable multipulse control, the nuclear-spin dynamics may be modeled to first approximation by a double-quantum one-dimensional Hamiltonian, which is analytically solvabl ... [Phys. Rev. A 80, 052323 (2009)] published Tue Nov 17, 2009.
Analytic approximations to the phase diagram of the Jaynes-Cummings-Hubbard model
Alexander Mering, Michael Fleischhauer, Peter A. Ivanov, and Kilian Singer
We discuss analytic approximations to the ground-state phase diagram of the homogeneous Jaynes-Cummings-Hubbard (JCH) Hamiltonian with general short-range hopping. The JCH model describes, e.g., radial phonon excitations of a linear chain of ions coupled to an external laser field tuned to the red m ... [Phys. Rev. A 80, 053821 (2009)] published Mon Nov 16, 2009.
Theory of two-dimensional macroscopic quantum tunneling in YBaCuO Josephson junctions coupled to an LC circuit
Shiro Kawabata, Thilo Bauch, and Takeo Kato
We investigate classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBaCuO (YBCO) Josephson junction coupled to an LC circuit theoretically. Due to the coupling between the junction and the LC circuit, the macroscopic phase dynamics can be described as the escape process o ... [Phys. Rev. B 80, 174513 (2009)] published Fri Nov 13, 2009.
Realization of Universal Ion-Trap Quantum Computation with Decoherence-Free Qubits
T. Monz, K. Kim, A. S. Villar, P. Schindler, M. Chwalla et al.
Any residual coupling of a quantum computer to the environment results in computational errors. Encoding quantum information in a so-called decoherence-free subspace provides means to avoid these errors. Despite tremendous progress in employing this technique to extend memory storage times by orders ... [Phys. Rev. Lett. 103, 200503 (2009)] published Fri Nov 13, 2009.
Decoherence Dynamics of Complex Photon States in a Superconducting Circuit
H. Wang, M. Hofheinz, M. Ansmann, R. C. Bialczak, Erik Lucero et al.
Quantum states inevitably decay with time into a probabilistic mixture of classical states due to their interaction with the environment and measurement instrumentation. We present the first measurement of the decoherence dynamics of complex photon states in a condensed-matter system. By controllabl ... [Phys. Rev. Lett. 103, 200404 (2009)] published Fri Nov 13, 2009.
Globally controlled universal quantum computation with arbitrary subsystem dimension
Gerardo A. Paz-Silva, Gavin K. Brennen, and Jason Twamley
We present a scheme to perform universal quantum computation using global control with an arbitrary subsystem dimension (not necessarily finite). The scheme is developed over a one spatial dimension N-element array, using only mirror-symmetric logical encoding, global pulses for single subsystem ope ... [Phys. Rev. A 80, 052318 (2009)] published Thu Nov 12, 2009.
Realization of topological quantum computation with planar codes
Su-Peng Kou
In this paper, the degenerate ground states of Z topological order on a plane with holes (the so-called planar codes) are used as the protected code subspace to build a topological quantum computer by tuning their quantum tunneling effect. Using a designer Hamiltonianthe Kitaev toric-code model as a ... [Phys. Rev. A 80, 052317 (2009)] published Thu Nov 12, 2009.
Genuine tripartite entanglement in quantum brachistochrone evolution of a three-qubit system
Bao-Kui Zhao, Fu-Guo Deng, Feng-Shou Zhang, and Hong-Yu Zhou
We explore the connection between quantum brachistochrone (time-optimal) evolution of a three-qubit system and its residual entanglement called three-tangle. The result shows that the entanglement between two qubits is not required for some brachistochrone evolutions of a three-qubit system. However ... [Phys. Rev. A 80, 052106 (2009)] published Wed Nov 11, 2009.
High-threshold universal quantum computation on the surface code
Austin G. Fowler, Ashley M. Stephens, and Peter Groszkowski
We present a comprehensive and self-contained simplified review of the quantum computing scheme of Raussendorf et al. [Phys. Rev. Lett. 98, 190504 (2007); N. J. Phys. 9, 199 (2007)], which features a two-dimensional nearest-neighbor coupled lattice of qubits, a threshold error rate approaching 1%, n ... [Phys. Rev. A 80, 052312 (2009)] published Wed Nov 11, 2009.
Measurement and compensation of optical Stark shifts for manipulating the terahertz-separated qubit in Ca
Shinsuke Haze, Rekishu Yamazaki, Kenji Toyoda, and Shinji Urabe
We describe the measurement and compensation of optical Stark shifts induced by an off-resonant pulse for manipulating the terahertz-separated states 3 D3 D, in a single trapped Ca ion. These states can be used as a quantum bit and are coupled by a two-photon stimulated Raman transition with phase-l ... [Phys. Rev. A 80, 053408 (2009)] published Wed Nov 11, 2009.
Learning and testing algorithms for the Clifford group
Richard A. Low
Given oracle access to an unknown unitary C from the Clifford group and its conjugate, we give an exact algorithm for identifying C with O(n) queries, which we prove is optimal. We then extend this to all levels of the Gottesman-Chuang hierarchy (also known as the [script C] hierarchy). Further, for ... [Phys. Rev. A 80, 052314 (2009)] published Wed Nov 11, 2009.
Geometric quantum gates in liquid-state NMR based on a cancellation of dynamical phases
Yukihiro Ota, Yoshito Goto, Yasushi Kondo, and Mikio Nakahara
A proposal for applying nonadiabatic geometric phases to quantum computing, called double-loop method [S.-L. Zhu and Z. D. Wang, Phys. Rev. A 67, 022319 (2003)], is demonstrated in a liquid-state nuclear magnetic-resonance quantum computer. Using a spin-echo technique, the original method is modifie ... [Phys. Rev. A 80, 052311 (2009)] published Tue Nov 10, 2009.
Erratum: Efficient quantum circuit implementation of quantum walks [Phys. Rev. A 79, 052335 (2009)]
B. L. Douglas and J. B. Wang
Abstract not available. [Phys. Rev. A 80, 059901 (2009)] published Tue Nov 10, 2009.
Geometric Entangling Gates in Decoherence-Free Subspaces with Minimal Requirements
Xun-Li Feng, Chunfeng Wu, Hui Sun, and C. H. Oh
We introduce a new strongly driven dispersive atom-cavity interaction and develop a new scheme for implementing the nontrivial entangling gates for two logical qubits in decoherence-free subspaces (DFSs). Our scheme combines the robust advantages of DFS and the geometric phase. Moreover, only two ne ... [Phys. Rev. Lett. 103, 200501 (2009)] published Tue Nov 10, 2009.
Weight of quadratic forms and graph states
Alessandro Cosentino and Simone Severini
We prove a connection between Schmidt rank and weight of quadratic forms. This provides a new tool for the classification of graph states based on entanglement. Our main tool arises from a reformulation of previously known results concerning the weight of quadratic forms in terms of graph states pro ... [Phys. Rev. A 80, 052309 (2009)] published Mon Nov 9, 2009.
Realizing singlet-triplet qubits in multivalley Si quantum dots
Dimitrie Culcer, Lukasz Cywinski, Qiuzi Li, Xuedong Hu, and S. Das Sarma
There has been significant progress in the implementation and manipulation of singlet-triplet qubits in GaAs quantum dots. Given the considerably longer spin coherence times measured in Si, considerable interest has been generated recently in Si quantum dots. The physics of these systems is consider ... [Phys. Rev. B 80, 205302 (2009)] published Thu Nov 5, 2009.
Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits
SangKook Choi, Dung-Hai Lee, Steven G. Louie, and John Clarke
The origin of magnetic flux noise in superconducting quantum interference devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuatin ... [Phys. Rev. Lett. 103, 197001 (2009)] published Tue Nov 3, 2009.
Equivalence between discrete quantum walk models in arbitrary topologies
F. M. Andrade and M. G. E. da Luz
Coin and scattering are the two major formulations for discrete quantum walks models, each believed to have its own advantages in different applications. Although they are related in some cases, it was an open question their equivalence in arbitrary topologies. Here we present a general construction ... [Phys. Rev. A 80, 052301 (2009)] published Mon Nov 2, 2009.