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Register a new userQuantum Zeno dynamics of a field in a cavity
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Added by
Jean-Michel Raimond
Publication date
2012
fields
Physics
and research's language is
English
Authors
Jean-Michel Raimond
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We analyze the quantum Zeno dynamics that takes place when a field stored in a cavity undergoes frequent interactions with atoms. We show that repeated measurements or unitary operations performed on the atoms probing the field state confine the evolution to tailored subspaces of the total Hilbert space. This confinement leads to non-trivial field evolutions and to the generation of interesting non-classical states, including mesoscopic field state superpositions. We elucidate the main features of the quantum Zeno mechanism in the context of a state-of-the-art cavity quantum electrodynamics experiment. A plethora of effects is investigated, from state manipulations by phase space tweezers to nearly arbitrary state synthesis. We analyze in details the practical implementation of this dynamics and assess its robustness by numerical simulations including realistic experimental imperfections. We comment on the various perspectives opened by this proposal.
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We have frozen the coherent evolution of a field in a cavity by repeated measurements of its photon number. We use circular Rydberg atoms dispersively coupled to the cavity mode for an absorption-free photon counting. These measurements inhibit the growth of a Field injected in the cavity by a classical source. This manifestation of the Quantum Zeno effect illustrates the back action of the photon number determination onto the Field phase. The residual growth of the Field can be seen as a random walk of its amplitude in the two-dimensional phase space. This experiment sheds light onto the measurement process and opens perspectives for active quantum feedback.
We discuss an implementation of Quantum Zeno Dynamics in a Cavity Quantum Electrodynamics experiment. By performing repeated unitary operations on atoms coupled to the field, we restrict the field evolution in chosen subspaces of the total Hilbert space. This procedure leads to promising methods for tailoring non-classical states. We propose to realize `tweezers picking a coherent field at a point in phase space and moving it towards an arbitrary final position without affecting other non-overlapping coherent components. These effects could be observed with a state-of-the-art apparatus.
A connection is estabilished between the non-Abelian phases obtained via adiabatic driving and those acquired via a quantum Zeno dynamics induced by repeated projective measurements. In comparison to the adiabatic case, the Zeno dynamics is shown to be more flexible in tuning the system evolution, which paves the way to the implementation of unitary quantum gates and applications in quantum control.
A new mechanism is proposed for dissipatively preparing maximal Bell entangled state of two atoms in an optical cavity. This scheme integrates the spontaneous emission, the light shift of atoms in the presence of dispersive microwave field, and the quantum Zeno dynamics induced by continuous coupling, to obtain a unique steady state irrespective of initial state. Even for a large cavity decay, a high-fidelity entangled state is achievable at a short convergence time, since the occupation of cavity mode is inhibited by the Zeno requirement. Therefore, a low single-atom cooperativity $C=g^2/(kappagamma)$ is good enough for realizing a high fidelity of entanglement in a wide range of decoherence parameters. As a straightforward extension, the feasibility for preparation of two-atom Knill-Laflamme-Milburn state with the same mechanism is also discussed.
We investigate the time evolution of an open quantum system described by a Lindblad master equation with dissipation acting only on a part of the degrees of freedom ${cal H}_0$ of the system, and targeting a unique dark state in ${cal H}_0$. We show that, in the Zeno limit of large dissipation, the density matrix of the system traced over the dissipative subspace ${cal H}_0$, evolves according to another Lindblad dynamics, with renormalized effective Hamiltonian and weak effective dissipation. This behavior is explicitly checked in the case of Heisenberg spin chains with one or both boundary spins strongly coupled to a magnetic reservoir. Moreover, the populations of the eigenstates of the renormalized effective Hamiltonian evolve in time according to a classical Markov dynamics. As a direct application of this result, we propose a computationally-efficient exact method to evaluate the nonequilibrium steady state of a general system in the limit of strong dissipation.
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