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Quantum Feedback Control Based on Entanglement Swapping

Dong Daoyi, Zonghai Chen

Published Nov 15, 2005• 0 citations
Publisher

Abstract

A scheme of quantum feedback control in which entanglement swapping is used to construct quantum feedback controller is proposed. The output state of the system to be controlled is entangled with the quantum state of a particle near the actuator through entanglement swapping, which constructs a quantum feedback channel, and two pairs of entangled states, two entanglement swapping processes and a unitary transformer together constitute a quantum controller. This feedback strategy can perform some tasks, such as remote control of entangled states and distant feedback of quantum states, which are not possible using quantum control with classical feedback.

DOI
10.1109/icca.2005.1528219

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A scheme of quantum feedback control in which entanglement swapping is used to construct quantum feedback controller is proposed. The output state of the system to be controlled is entangled with the quantum state of a particle near the actuator through entanglement swapping, which constructs a quantum feedback channel, and two pairs of entangled states, two entanglement swapping processes and a unitary transformer together constitute a quantum controller. This feedback strategy can perform some tasks, such as remote control of entangled states and distant feedback of quantum states, which are not possible using quantum control with classical feedback.
In the conventional picture of quantum feedback control, sensors perform measurements on the system, a classical controller processes the results of the measurements, and actuators supply semiclassical potentials to alter the behavior of the quantum system. In this picture, the sensors tend to destroy coherence in the process of making measurements, and although the controller can use the actuators to act coherently on the quantum system, it is processing and feeding back classical information. This paper proposes an alternative method for quantum feedback control, in which the sensors, controller, and actuators are quantum systems that interact coherently with the system to be controlled. In this picture, the controller gets, processes, and feeds back quantum information. Controllers that operate using such quantum feedback loops can perform tasks such as entanglement transfer that are not possible using classical feedback. Necessary and sufficient conditions are presented for Hamiltonian quantum systems to be controllable and observable using both classical and quantum feedback.
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In the conventional picture of quantum feedback control, sensors make measurements on a quantum system, a classical controller processes the results of the measurements, and semi-classical actuators act back on the system to alter its behavior. Quantum measurements are well known to yield probabilistic results and to introduce unavoidable disturbances in the system measured. Accordingly, quantum feedback is traditionally considered to be both probabilistic and destructive. This paper proposes and provides an experimental demonstration of an alternative method for quantum feedback control, in which sensors, controller, and actuators are themselves quantum systems that interact coherently with the system to be controlled. The resulting feedback loop preserves quantum coherence. Such coherent quantum feedback control is deterministic, non-destructive, and can be used to perform actions such as transferring quantum entanglement that are not possible using conventional feedback control of quantum systems. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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When a quantum system interacts with its environment, the so-called decoherence effect will normally destroy the coherence in the quantum state and the entanglement between its subsystems. We propose a feedback control strategy based on quantum weak measurements to protect coherence and entanglement of the quantum state against environmental disturbance. For a one-qubit quantum system under amplitude damping and dephasing decoherence channels, our strategy can preserve the coherence based on the measured information about the population difference between its two levels. For a two-qubit quantum system disentangled by independent amplitude damping and dephasing decoherence channels, the designed feedback control can preserve coherence between the ground state and the highest excited states by tuning the coupling strength between the two qubits, and at the same time minimize the loss of entanglement between the two qubits. As a consequence of dynamic symmetry, the generalization of these results derives the concept of control-induced decoherence-free observable subspace, for which several criteria are provided.