Search results for "quant-ph"
showing 10 items of 1378 documents
Quantifying nonclassicality: global impact of local unitary evolutions
2012
We show that only those composite quantum systems possessing nonvanishing quantum correlations have the property that any nontrivial local unitary evolution changes their global state. We derive the exact relation between the global state change induced by local unitary evolutions and the amount of quantum correlations. We prove that the minimal change coincides with the geometric measure of discord (defined via the Hilbert- Schmidt norm), thus providing the latter with an operational interpretation in terms of the capability of a local unitary dynamics to modify a global state. We establish that two-qubit Werner states are maximally quantum correlated, and are thus the ones that maximize t…
Entanglement in continuous-variable systems: recent advances and current perspectives
2007
We review the theory of continuous-variable entanglement with special emphasis on foundational aspects, conceptual structures, and mathematical methods. Much attention is devoted to the discussion of separability criteria and entanglement properties of Gaussian states, for their great practical relevance in applications to quantum optics and quantum information, as well as for the very clean framework that they allow for the study of the structure of nonlocal correlations. We give a self-contained introduction to phase-space and symplectic methods in the study of Gaussian states of infinite-dimensional bosonic systems. We review the most important results on the separability and distillabil…
Bicoherent-State Path Integral Quantization of a non-Hermitian Hamiltonian
2020
We introduce, for the first time, bicoherent-state path integration as a method for quantizing non-hermitian systems. Bicoherent-state path integrals arise as a natural generalization of ordinary coherent-state path integrals, familiar from hermitian quantum physics. We do all this by working out a concrete example, namely, computation of the propagator of a certain quasi-hermitian variant of Swanson's model, which is not invariant under conventional $PT$-transformation. The resulting propagator coincides with that of the propagator of the standard harmonic oscillator, which is isospectral with the model under consideration by virtue of a similarity transformation relating the corresponding…
Space and Time Averaged Quantum Stress Tensor Fluctuations
2021
We extend previous work on the numerical diagonalization of quantum stress tensor operators in the Minkowski vacuum state, which considered operators averaged in a finite time interval, to operators averaged in a finite spacetime region. Since real experiments occur over finite volumes and durations, physically meaningful fluctuations may be obtained from stress tensor operators averaged by compactly supported sampling functions in space and time. The direct diagonalization, via a Bogoliubov transformation, gives the eigenvalues and the probabilities of measuring those eigenvalues in the vacuum state, from which the underlying probability distribution can be constructed. For the normal-orde…
Global-to-local incompatibility, monogamy of entanglement, and ground-state dimerization: Theory and observability of quantum frustration in systems …
2015
Frustration in quantum many body systems is quantified by the degree of incompatibility between the local and global orders associated, respectively, to the ground states of the local interaction terms and the global ground state of the total many-body Hamiltonian. This universal measure is bounded from below by the ground-state bipartite block entanglement. For many-body Hamiltonians that are sums of two-body interaction terms, a further inequality relates quantum frustration to the pairwise entanglement between the constituents of the local interaction terms. This additional bound is a consequence of the limits imposed by monogamy on entanglement shareability. We investigate the behavior …
Quantum walk on a cylinder
2016
We consider the 2D alternate quantum walk on a cylinder. We concentrate on the study of the motion along the open dimension, in the spirit of looking at the closed coordinate as a small or "hidden" extra dimension. If one starts from localized initial conditions on the lattice, the dynamics of the quantum walk that is obtained after tracing out the small dimension shows the contribution of several components, which can be understood from the study of the dispersion relations for this problem. In fact, these components originate from the contribution of the possible values of the quasi-momentum in the closed dimension. In the continuous space-time limit, the different components manifest as …
Analysis of high excited "hot" bands of the SO2 molecule
2011
The main goal of the present study is to analyse rotational structures of highly excited "hot" vibrational bands, v1+2v2-v2 and 2v2+v3-v2, v2+3v3-v2 and 2v1+v2+v3-v2, and v2+2v3-v2. All of these bands are located in the region of considerably stronger bands, v1 + v2 and v2 + v3, 3v3 and 2v1+v3, and 2v3, respectively . On that reason, as the first step of analysis, we made assignments of transitions belonging to these strong bands. As the result of analysis, we were able to assign three times more transitions to the bands v1 + v2 , v2 + v3, and 3v3 (3360 transitions with Jmax. = 78 and Kmax.a = 27 to the band v1 + v2, and 2380 transitions with Jmax. = 69 and Kmax.a = 24 to the band v2 + v3, …
Vibrational modes of the stibine molecule
2005
International audience; In this paper, we use the algebraic approach to describe the vibrational modes of stibine molecule (of C3v molecular symmetry group) up to 21 quanta. As the stibine molecule exhibits stretch-bend resonances, we build an algebraic pyramidal coupling operator between stretching modes and bending modes adapted to this molecule. The standard deviation associated to the fit of the vibrational levels is 1.75 cm-1.
Quantum search of spatial regions
2003
Can Grover's algorithm speed up search of a physical region - for example a 2-D grid of size sqrt(n) by sqrt(n)? The problem is that sqrt(n) time seems to be needed for each query, just to move amplitude across the grid. Here we show that this problem can be surmounted, refuting a claim to the contrary by Benioff. In particular, we show how to search a d-dimensional hypercube in time O(sqrt n) for d at least 3, or O((sqrt n)(log n)^(3/2)) for d=2. More generally, we introduce a model of quantum query complexity on graphs, motivated by fundamental physical limits on information storage, particularly the holographic principle from black hole thermodynamics. Our results in this model include a…
High Resolution Study of the v1 + 2v2 −v2 and 2v2 + v3 − v2 ”Hot” Bands and Ro-Vibrational Re-Analysis of the v1 + v2/v2 + v3/3v3 Poliad of the SO2 M…
2010
The main goal of the present study was to analyse rotational stuctures of two excited vibrational states, (120) and (021). Because both the band, v1+2v2 and 2v2+v3 one are extremally weak, a special efforts were faired to record very weak hot bands, v1+2v2−v2 and 2v2+v3−v2.Both of those bands are located in the region of considerably more stronger combinational bands, v1 + v2 and v2 + v3. On that reason, as the first step of analysis, we made assignments of transitions belonging to these v1 + v2 and v2 + v3 bands. As the result of analysis, we were able to assign three times more transitions to the bands v1 + v2 and v2 + v3 than it was known in the before literature. After "cleaning" the ex…