6 research outputs found
Real-time Information, Uncertainty and Quantum Feedback Control
Feedback is the core concept in cybernetics and its effective use has made
great success in but not limited to the fields of engineering, biology, and
computer science. When feedback is used to quantum systems, two major types of
feedback control protocols including coherent feedback control (CFC) and
measurement-based feedback control (MFC) have been developed. In this paper, we
compare the two types of quantum feedback control protocols by focusing on the
real-time information used in the feedback loop and the capability in dealing
with parameter uncertainty. An equivalent relationship is established between
quantum CFC and non-selective quantum MFC in the form of operator-sum
representation. Using several examples of quantum feedback control, we show
that quantum MFC can theoretically achieve better performance than quantum CFC
in stabilizing a quantum state and dealing with Hamiltonian parameter
uncertainty. The results enrich understanding of the relative advantages
between quantum MFC and quantum CFC, and can provide useful information in
choosing suitable feedback protocols for quantum systems.Comment: 24 page
On the dynamics of two photons interacting with a two-qubit coherent feedback network}
The purpose of this paper is to study the dynamics of a quantum coherent
feedback network composed of two two-level systems (qubits) driven by two
counter-propagating photons, one in each input channel. The coherent feedback
network enhances the nonlinear photon-photon interaction inside the feedback
loop. By means of quantum stochastic calculus and the input-output framework,
the analytic form of the steady-state output two-photon state is derived. Based
on the analytic form, the applications on the Hong-Ou-Mandel (HOM)
interferometer and marginally stable single-photon devices using this coherent
feedback structure have been demonstrated. The difference between
continuous-mode and single-mode few-photon states is demonstrated.Comment: 15 pages, 4 figures; accepted by Automatica; comments are welcome
Sampling-based Learning Control for Quantum Systems with Uncertainties
Robust control design for quantum systems has been recognized as a key task
in the development of practical quantum technology. In this paper, we present a
systematic numerical methodology of sampling-based learning control (SLC) for
control design of quantum systems with uncertainties. The SLC method includes
two steps of "training" and "testing". In the training step, an augmented
system is constructed using artificial samples generated by sampling
uncertainty parameters according to a given distribution. A gradient flow based
learning algorithm is developed to find the control for the augmented system.
In the process of testing, a number of additional samples are tested to
evaluate the control performance where these samples are obtained through
sampling the uncertainty parameters according to a possible distribution. The
SLC method is applied to three significant examples of quantum robust control
including state preparation in a three-level quantum system, robust
entanglement generation in a two-qubit superconducting circuit and quantum
entanglement control in a two-atom system interacting with a quantized field in
a cavity. Numerical results demonstrate the effectiveness of the SLC approach
even when uncertainties are quite large, and show its potential for robust
control design of quantum systems.Comment: 11 pages, 9 figures, in press, IEEE Transactions on Control Systems
Technology, 201
Analysis of Quantum Linear Systems' Response to Multi-photon States
The purpose of this paper is to present a mathematical framework for
analyzing the response of quantum linear systems driven by multi-photon states.
Both the factorizable (namely, no correlation among the photons in the channel)
and unfactorizable multi-photon states are treated. Pulse information of
multi-photon input state is encoded in terms of tensor, and response of quantum
linear systems to multi-photon input states is characterized by tensor
operations. Analytic forms of output correlation functions and output states
are derived. The proposed framework is applicable no matter whether the
underlying quantum dynamic system is passive or active. The results presented
here generalize those in the single-photon setting studied in (Milburn, 2008)
and (Zhang and James, 2013}). Moreover, interesting multi-photon interference
phenomena studied in (Sanaka, Resch, and Zeilinger, 2006), (Ou, 2007), and
(Bartley, et al., 2012) can be reproduced in the proposed frameworkComment: 26 pages, 2 figures, accepted by Automatic