1,426 research outputs found
Transition Amplitudes within the Stochastic Quantization Scheme
Quantum mechanical transition amplitudes are calculated within the stochastic
quantization scheme for the free nonrelativistic particle, the harmonic
oscillator and the nonrelativistic particle in a constant magnetic field; we
close with free Grassmann quantum mechanics.Comment: 14 pages, LaTeX, UWThPh-1993-23 and DPUR 6
Completeness of scattering states of the Dirac Hamiltonian with a step potential
The completeness, together with the orthonormality, of the eigenfunctions of
the Dirac Hamiltonian with a step potential is shown explicitly. These
eigenfunctions describe the scattering process of a relativistic fermion off
the step potential and the resolution of the identity in terms of them
(completeness) is shown by explicitly summing them up, where appropriate
treatments of the momentum integrations are crucial. The result would bring
about a basis on which a field theoretical treatment for such a system can be
developed.Comment: 16 pages, 1 figure
Exactly solvable time-dependent models of two interacting two-level systems
Two coupled two-level systems placed under external time-dependent magnetic
fields are modeled by a general Hamiltonian endowed with a symmetry that
enables us to reduce the total dynamics into two independent two-dimensional
sub-dynamics. Each of the sub-dynamics is shown to be brought into an exactly
solvable form by appropriately engineering the magnetic fields and thus we
obtain an exact time evolution of the compound system. Several physically
relevant and interesting quantities are evaluated exactly to disclose
intriguing phenomena in such a system.Comment: 15 pages, 13 figure
Synchronizing Quantum Harmonic Oscillators through Two-Level Systems
Two oscillators coupled to a two-level system which in turn is coupled to an
infinite number of oscillators (reservoir) are considered, bringing to light
the occurrence of synchronization. A detailed analysis clarifies the physical
mechanism that forces the system to oscillate at a single frequency with a
predictable and tunable phase difference. Finally, the scheme is generalized to
the case of oscillators and two-level systems.Comment: 9 pages, 3 figure
From the quantum Zeno to the inverse quantum Zeno effect
The temporal evolution of an unstable quantum mechanical system undergoing
repeated measurements is investigated. In general, by changing the time
interval between successive measurements, the decay can be accelerated (inverse
quantum Zeno effect) or slowed down (quantum Zeno effect), depending on the
features of the interaction Hamiltonian. A geometric criterion is proposed for
a transition to occur between these two regimes.Comment: 6 pages, 3 figure
Resonant Scattering Can Enhance the Degree of Entanglement
Generation of entanglement between two qubits by scattering an entanglement
mediator is discussed. The mediator bounces between the two qubits and exhibits
a resonant scattering. It is clarified how the degree of the entanglement is
enhanced by the constructive interference of such bouncing processes. Maximally
entangled states are available via adjusting the incident momentum of the
mediator or the distance between the two qubits, but their fine tunings are not
necessarily required to gain highly entangled states and a robust generation of
entanglement is possible.Comment: 7 pages, 13 figure
Heat Capacity and Entanglement Measure in a simple two-qubit model
A simple two-qubit model showing Quantum Phase Transitions as a consequence
of ground state level crossings is studied in detail. Using the Concurrence of
the system as an entanglement measure and heat capacity as a marker of
thermodynamical properties, an analytical expression giving the latter in terms
of the former is obtained. A protocol allowing an experimental measure of
entanglement is then presented and compared with a related proposal recently
reported by Wie\'sniak, Vedral and BruknerComment: 7 pages, 3 figure
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