Variational Numerical Renormalization Group: Bridging the Gap between NRG and Density Matrix Renormalization Group
Iztok Pizorn and Frank Verstraete
The numerical renormalization group (NRG) is rephrased as a variational method with the cost function given by the sum of all the energies of the effective low-energy Hamiltonian. This allows us to systematically improve the spectrum obtained by NRG through sweeping. The ensuing algorithm has a lot ... [Phys. Rev. Lett. 108, 067202 ] published .
Experimental Estimate of a Classicality Witness via a Single Measurement
G. H. Aguilar, O. Jimenez Farias, J. Maziero, R. M. Serra, P. H. Souto Ribeiro et al.
The perception that quantum correlations can still appear in separable states has opened exciting new possibilities regarding their use as a resource in quantum information science. Quantifying such quantum correlations involves the complete knowledge of the system's state and numerical optimization ... [Phys. Rev. Lett. 108, 063601 ] published .
Overcoming decoherence in the collapse and revival of spin Schrodinger-cat states
M. J. Everitt, W. J. Munro, and T. P. Spiller
In addition to being a very interesting quantum phenomenon, Schrodinger-cat-state swapping has the potential for application in the preparation of quantum states that could be used in metrology and other quantum processing. We study in detail the effects of field decoherence on a Schrodinger-cat-sta ... [Phys. Rev. A 85, 022113 ] published .
NMR implementation of a quantum delayed-choice experiment
Soumya Singha Roy, Abhishek Shukla, and T. S. Mahesh
We report an experimental demonstration of a quantum delayed-choice experiment via nuclear magnetic resonance techniques. Two spin-1/2 nuclei from each molecule of a liquid ensemble are used as target and ancilla qubits. The circuit corresponding to the recently proposed quantum delayed-choice setup ... [Phys. Rev. A 85, 022109 ] published .
Observers can always generate nonlocal correlations without aligning measurements by covering all their bases
Joel J. Wallman and Stephen D. Bartlett
Quantum theory allows for correlations between the outcomes of distant measurements that are inconsistent with any locally causal model, as demonstrated by the violation of a Bell inequality. Typical demonstrations of these correlations require careful alignment between the measurements, which requi ... [Phys. Rev. A 85, 024101 ] published .
Entanglement spectra of coupled S=(1/2) spin chains in a ladder geometry
Andreas M. Lauchli and John Schliemann
We study the entanglement spectrum of spin-1/2 XXZ ladders both analytically and numerically. Our analytical approach is based on perturbation theory starting either from the limit of strong rung coupling, or from the opposite case of dominant coupling along the legs. In the former case we find to l ... [Phys. Rev. B 85, 054403 ] published .
Matrix product state based algorithm for determining dispersion relations of quantum spin chains with periodic boundary conditions
B. Pirvu, J. Haegeman, and F. Verstraete
We study a matrix product state algorithm to approximate excited states of translationally invariant quantum spin systems with periodic boundary conditions. By means of a momentum eigenstate ansatz generalizing the one of Ostlund and Rommer [see S. Ostlund and S. Rommer, Phys. Rev. Lett. 75, 3537 (1 ... [Phys. Rev. B 85, 035130 ] published .
Evaluation of weak measurements to all orders
Kouji Nakamura, Atsushi Nishizawa, and Masa-Katsu Fujimoto
Some exact formulas of the expectation values and probability densities in a weak measurement for an operator A that satisfies the property A=1 are derived. These formulas include all-order effects of the unitary evolution due to the von Neumann interaction. These are valid not only in the weak-meas ... [Phys. Rev. A 85, 012113 ] published .
Informationally complete joint measurements on finite quantum systems
Claudio Carmeli, Teiko Heinosaari, and Alessandro Toigo
We show that there are informationally complete joint measurements of two conjugated observables on a finite quantum system, meaning that they enable the identification of all quantum states from their measurement outcome statistics. We further demonstrate that it is possible to implement a joint ob ... [Phys. Rev. A 85, 012109 ] published .
Nuclear Spins of Ionized Phosphorus Donors in Silicon
Lukas Dreher, Felix Hoehne, Martin Stutzmann, and Martin S. Brandt
We demonstrate the coherent control and electrical readout of ionized phosphorus donor nuclear spins in Si. By combining time-programed optical excitation with coherent electron spin manipulation, we selectively ionize the donors depending on their nuclear spin state, exploiting a spin-dependent rec ... [Phys. Rev. Lett. 108, 027602 ] published .
Measuring which-path information with coupled electronic Mach-Zehnder interferometers
J. Dressel, Y. Choi, and A. N. Jordan
We theoretically investigate a generalized which-path measurement on an electronic Mach-Zehnder Interferometer (MZI) implemented via Coulomb coupling to a second electronic MZI acting as a detector. The use of contextual values, or generalized eigenvalues, enables the precise construction of which-p ... [Phys. Rev. B 85, 045320 ] published .
Edge-mode combinations in the entanglement spectra of non-Abelian fractional quantum Hall states on the torus
Zhao Liu, Emil J. Bergholtz, Heng Fan, and Andreas M. Lauchli
We present a detailed analysis of bipartite entanglement in the non-Abelian Moore-Read fractional quantum Hall state of bosons and fermions on the torus. In particular, we show that the entanglement spectra can be decomposed into intricate combinations of different sectors of the conformal field the ... [Phys. Rev. B 85, 045119 ] published .
Quantum memory with a single two-level atom in a half cavity
Yimin Wang, Jiri Minar, Gabriel Hetet, and Valerio Scarani
We propose a setup for quantum memory based on a single two-level atom in a half cavity with a moving mirror. We show that various temporal shapes of incident photon can be efficiently stored and read out by shaping the time-dependent decay rate gamma(t) between the atom and the light. This is achie ... [Phys. Rev. A 85, 013823 ] published .
Thermodynamic behavior of the quantum walk
Alejandro Romanelli
A thermodynamic theory is developed to describe the behavior of the entanglement between the coin and position degrees of freedom of the quantum walk on the line. It is shown that, in spite of the unitary evolution, a steady state is established after a Markovian transient stage. This study suggests ... [Phys. Rev. A 85, 012319 ] published .
Significance of the imaginary part of the weak value
J. Dressel and A. N. Jordan
Unlike the real part of the generalized weak value of an observable, which can in a restricted sense be operationally interpreted as an idealized conditioned average of that observable in the limit of zero measurement disturbance, the imaginary part of the generalized weak value does not provide inf ... [Phys. Rev. A 85, 012107 ] published .
Monogamy of quantum correlations in three-qubit pure states
Sudha, A. R. Usha Devi, and A. K. Rajagopal
The limitation on the shareability of quantum entanglement over several parties, the so-called monogamy of entanglement, is an issue that has received considerable attention from the quantum information community over the last decade. A natural question of interest in this connection is whether mono ... [Phys. Rev. A 85, 012103 ] published .
Two-qubit parametric amplifier: Large amplification of weak signals
S. Savel'ev, A. M. Zagoskin, A. L. Rakhmanov, A. N. Omelyanchouk, Z. Washington et al.
Using numerical simulations, we show that two coupled qubits can amplify a weak signal about a hundredfold. This can be achieved if the two qubits are biased simultaneously by this weak signal and a strong pump signal, both having frequencies close to the interlevel transitions in the system. The we ... [Phys. Rev. A 85, 013811 ] published .
Experimental implementation of unambiguous quantum reading
Michele Dall'Arno, Alessandro Bisio, Giacomo Mauro D'Ariano, Martina Mikova, Miroslav Jezek et al.
We provide the optimal strategy for the unambiguous quantum reading of optical memories, namely when perfect retrieving of information is achieved probabilistically, for the case where noise and loss are negligible. We describe the experimental quantum optical implementations, and provide experiment ... [Phys. Rev. A 85, 012308 ] published .
Spin Relaxation near the Metal-Insulator Transition: Dominance of the Dresselhaus Spin-Orbit Coupling
Guido A. Intronati, Pablo I. Tamborenea, Dietmar Weinmann, and Rodolfo A. Jalabert
We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are sh ... [Phys. Rev. Lett. 108, 016601 ] published .
Quantum discord and classical correlations in the bond-charge Hubbard model: Quantum phase transitions, off-diagonal long-range order, and violation of the monogamy property for discord
Michele Allegra, Paolo Giorda, and Arianna Montorsi
We study the quantum discord (QD) and the classical correlations (CC) in a reference model for strongly correlated electrons, the one-dimensional bond-charge extended Hubbard model. We show that the comparison of QD and CC and of their derivatives in the direct and reciprocal lattice allows one to e ... [Phys. Rev. B 84, 245133 ] published .
Adaptive schemes for incomplete quantum process tomography
Yong Siah Teo, Berthold-Georg Englert, Jaroslav RehaCek, and Zdenek Hradil
We propose an iterative algorithm for incomplete quantum process tomography with the help of quantum state estimation. The algorithm, which is based on the combined principles of maximum likelihood and maximum entropy, yields a unique estimator for an unknown quantum process when one has less than a ... [Phys. Rev. A 84, 062125 ] published .