Controlling quantum state reductions

Joshua Combes, Kurt A. Jacobs

We consider using Hamiltonian feedback control to increase the speed at which a continuous measurement purifies (reduces) the state of a quantum system, and thus to increase the speed of the preparation of pure states. For a measurement of an observable with equispaced eigenvalues, we show that there exists a feedback algorithm which will speed up the rate of state reduction by at least a factor of 2(N + 1)/3.

Shan Gao

Thanh Long Vu, Shuzhi Sam Ge, Chang Chieh Hang

We exploit our recently introduced concept of SWM- (simultaneous weak measurements)-induced quantum state reduction, enabling the use of multiple measurements to produce the desired quantum states. The probabilistic generation of the maximally entangled Bell states is then performed as a consequence of this concept. By combining SWM-induced quantum state reduction with feedback control, we are able to deterministically generate any desired Bell state, without the knowledge of initial state. The control-computation time is compensated for by the delay time in the time delay bang-bang control, through which the real-time implementation of the control scheme is guaranteed. The effectiveness of the proposed scheme is illustrated numerically.

Masanao Ozawa

正直 小澤

Thanh Long Vu, Jaspreet Singh Dhupia

We present a realtime feedback control scheme to deterministically produce the maximally entangled Bell states of two partially separated atoms. The recently introduced concept of SWM- (simultaneous weak measurements)-induced quantum state reduction is generalized to the case of anti-commutative observables. This generalization enables the probabilistic preparation of the Bell states via the SWMs of one linear observable and one nonlocal observable. The deterministic generation of the desired Bell state is then carried out by combining SWM-induced quantum state reduction with feedback control. The realtime implementation of the proposed control scheme is guaranteed by using the time delay control approach in which the computation time of filter-based control is compensated for by the delay time in control input.