Sanjib Dey, Andreas Fring, Laure Gouba, Paulo G. Castro
We investigate properties of generalized time-dependent q-deformed coherent states for a noncommutative harmonic oscillator. The states are shown to satisfy a generalized version of Heisenberg’s uncertainty relations. For the initial value in time the states are demonstrated to be squeezed, i.e. the inequalities are saturated, whereas when time evolves the uncertainty product oscillates away from this value albeit still respecting the relations. For the canonical variables on a noncommutative space we verify explicitly that Ehrenfest’s theorem hold at all times. We conjecture that the model exhibits revival times to infinite order. Explicit sample computations for the fractional revival times and superrevival times are presented.
http://arxiv.org/abs/1211.4791
Mathematical Physics (math-ph); High Energy Physics – Theory (hep-th); Quantum Physics (quant-ph)
Miloslav Znojil
The quantum-catastrophe (QC) benchmark Hamiltonians of paper I (M. Znojil, J. Phys. A: Math. Theor. 45 (2012) 444036) are reconsidered, with the infinitesimal QC distance \(\lambda\) replaced by the total time $\tau$ of the fall into the singularity. Our amended model becomes unique, describing the complete QC history as initiated by a Hermitian and diagonalized N-level oscillator Hamiltonian at \(\tau=0\). In the limit \(\tau \to 1\) the system finally collapses into the completely (i.e., N-times) degenerate QC state. The closed and compact Hilbert-space metrics are then calculated and displayed up to N=7. The phenomenon of the QC collapse is finally attributed to the manifest time-dependence of the Hilbert space and, in particular, to the emergence and to the growth of its anisotropy. A quantitative measure of such a time-dependent anisotropy is found in the spread of the N-plet of the eigenvalues of the metric. Unexpectedly, the model appears exactly solvable — at any multiplicity N, the N-plet of these eigenvalues is obtained in closed form.
http://arxiv.org/abs/1212.0734
Quantum Physics (quant-ph); Mathematical Physics (math-ph)
X. Z. Zhang, L. Jin, Z. Song
Complex potential and non-Hermitian hopping amplitude are building blocks of a non-Hermitian quantum network. Appropriate configuration, such as PT-symmetric distribution, can lead to the full real spectrum. To investigate the underlying mechanism of this phenomenon, we study the phase diagram of a semi-infinite non-Hermitian system. It consists of a finite non-Hermitian cluster and a semi-infinite lead. Based on the analysis of the solution of the concrete systems, it is shown that it can have the full real spectrum without any requirements on the symmetry and the wave function within the lead becomes a unidirectional plane wave at the exceptional point. This universal dynamical behavior is demonstrated as the persistent emission and reflectionless absorption of wave packets in the typical non-Hermitian systems containing the complex on-site potential and non-Hermitian hopping amplitude.
http://arxiv.org/abs/1212.0086
Quantum Physics (quant-ph)
Belal E. Baaquie
The Euclidean action with acceleration has been analyzed in [1], hereafter cited as reference I, for its Hamiltonian and path integral. In this paper, the state space of the Hamiltonian is analyzed for the case when it is pseudo-Hermitian (equivalent to a Hermitian Hamiltonian), as well as the case when it is inequivalent. The propagator is computed using both creation/destruction operators as well as the path integral. A state space calculation of the propagator shows the crucial role played by the dual state vectors that yields a result impossible to obtain from a Hermitian Hamiltonian acting on a Hilbert space. When it is not pseudo-Hermitian, the Hamiltonian is shown to be a direct sum of Jordan blocks.
http://arxiv.org/abs/1211.7166
Quantum Physics (quant-ph); Mathematical Physics (math-ph)
Belal E. Baaquie
An action having an acceleration term in addition to the usual velocity term is analyzed. The quantum mechanical system is directly defined for Euclidean time using the path integral. The Euclidean Hamiltonian is shown to yield the acceleration Lagrangian and the path integral with the correct boundary conditions. Due to the acceleration term, the state space depends on both position and velocity, and hence the Euclidean Hamiltonian depends on two degrees of freedom. The Hamiltonian for the acceleration system is non-Hermitian and can be mapped to a Hermitian Hamiltonian using a similarity transformation; the matrix elements of this unbounded transformation is explicitly evaluated. The mapping fails for a critical value of the coupling constants.
http://arxiv.org/abs/1211.7168
Quantum Physics (quant-ph); Mathematical Physics (math-ph)
D.E. Pelinovsky, P.G. Kevrekidis, D.J. Frantzeskakis
We illustrate, through a series of prototypical examples, that linear parity-time (PT) symmetric lattices with extended gain/loss profiles are generically unstable, for any non-zero value of the gain/loss coefficient. Our examples include a parabolic real potential with a linear imaginary part and the cases of no real and constant or linear imaginary potentials. On the other hand, this instability can be avoided and the spectrum can be real for localized or compact PT-symmetric potentials. The linear lattices are analyzed through discrete Fourier transform techniques complemented by numerical computations.
http://arxiv.org/abs/1211.5815
Exactly Solvable and Integrable Systems (nlin.SI); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
Rujiang Li, Pengfei Li, Lu Li
We design and optimize a waveguide structure consisted of three segments of PT-symmetric coupler. It can amplify the difference mode with the attenuation of the sum mode, so performs an asymmetric optical amplifier. Also, the dependence of the amplification factor for the difference mode and the attenuation factor for the sum mode on the gain/loss is illustrated.
http://arxiv.org/abs/1211.4296
Optics (physics.optics)
Yuliy V. Bludov, Vladimir V. Konotop, Boris A. Malomed
We construct dark solitons in the recently introduced model of the nonlinear dual-core coupler with the mutually balanced gain and loss applied to the two cores, which is a realization of parity-time symmetry in nonlinear optics. The main issue is stability of the dark solitons. The modulational stability of the CW (continuous-wave) background, which supports the dark solitons, is studied analytically, and the full stability is investigated in a numerical form, via computation of eigenvalues for modes of small perturbations. Stability regions are thus identified in the parameter space of the system, and verified in direct simulations. Collisions between stable dark solitons are briefly considered too.
http://arxiv.org/abs/1211.3746
Optics (physics.optics); Pattern Formation and Solitons (nlin.PS)
Alexander I. Nesterov, Juan Carlos Beas Zepeda, Gennady P. Berman
We create a non-Hermitian quantum optimization algorithm to find the ground state of an Ising model with up to 1024 spins (qubits). Our approach leads to significant reduction of the annealing time. Analytic and numerical results demonstrate that the total annealing time is proportional to ln N, where N is the number of spins. This encouraging result is important for the rapid solution of NP-complete problems. Additional research is proposed for extending our dissipative algorithm to more complicated problems.
http://arxiv.org/abs/1211.3178
Quantum Physics (quant-ph); Mathematical Physics (math-ph); Computational Physics (physics.comp-ph)
P. E. G. Assis
We study the spectral correspondence between a particular class of Schrodinger equations and supersymmetric quantum integrable model (QIM). The latter, a quantized version of the Ablowitz-Kaupp-Newell-Segur (AKNS) hierarchy of nonlinear equations, corresponds to the thermodynamic limit of the Perk-Schultz lattice model. By analyzing the symmetries of the ordinary differential equation (ODE) in the complex plane, it is possible to obtain important objects in the quantum integrable model in exact form, under an exact spectral correspondence. In this manuscript our main interest lies on the set of nonlocal conserved inte- grals of motion associated to the integrable system and we provide a systematic method to compute their values evaluated on the vacuum state of the quantum field theory.
http://arxiv.org/abs/1211.2397
High Energy Physics – Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)