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International Conference on Quantum, Nano and Micro Technologies (ICQNM)

Quantum-Zeno Control of Collisional Entanglement in a Bose-Josephson Junction

Amichay Vardi, Yuri Khodorkovsky, Gershon Kurizki

Published Feb 1, 2009• 1 citation
Publisher

Abstract

We propose a scheme to control the collision-induced entanglement between atoms in the two-site Bose-Hubbard model, by means of site-indiscriminate noise. This decoherence mechanism induces the continuous measurement of the quasi-momentum, protecting single-particle coherence via a Bose-enhanced many-body Quantum-Zeno effect.
DOI
10.1109/icqnm.2009.17

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The quantum Zeno effect is a distinctive phenomenon in quantum mechanics, describing the nontrivial effect of frequent projective measurements on hindering the evolution of a quantum system. However, when subjected to environmental noise, the quantum system may dissipate, and the quantum Zeno effect no longer works. This research starts from the physical mechanism for the decay of the quantum Zeno effect in the presence of noise and investigates the effect of coherent quantum controls on mitigating the decrease of the survival probability that the system stays in the initial state induced by the noise. We derive the decay rate of the survival probability with and without coherent quantum controls in general, and show that when the frequency of the projective measurements is large but finite, proper coherent controls by sufficiently strong Hamiltonians can be designed to decrease the decay rate of the survival probability. A two-level quantum system suffering from typical unitary and nonunitary noise is then considered to demonstrate the effect of the proposed coherent quantum control scheme in protecting the quantum Zeno effect against the noise. The decay rate of the survival probability is obtained in the presence of noise, and the control Hamiltonian is further optimized analytically to minimize the decay rate by a variational approach. The evolution paths of the quantum system with the optimal coherent controls are illustrated numerically for different scenarios to explicitly show how the coherent control scheme works in lowering the decay of survival probability.
We propose an experiment to observe the quantum Zeno effect in atomic Bragg scattering. The quantum Zeno effect is the inhibition of the free evolution of a system when that system is subject to a decohering measurement process. This effect is usually studied theoretically in an idealized two-level system, though this system has been difficult to realize in practice. The coherent population exchange between the forward and Bragg beams provides an ideal two-level system, though as there is no practical scheme for continuously monitoring the motion of an atom we include decoherence by adding noise to the laser. Using the method of stochastic Hamiltonians we show that the noise suppresses tunneling in the two-state system and, in the large noise limit, the system can freeze in its initial state.
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