Feedback control of a non-Markovian single qubit system

Author(s):  
Shibei Xue ◽  
Thien Nguyen ◽  
Ian R. Petersen
2008 ◽  
Vol 06 (supp01) ◽  
pp. 645-650 ◽  
Author(s):  
A. MASTELLONE ◽  
A. D'ARRIGO ◽  
E. PALADINO ◽  
G. FALCI

We discuss the effect of low-frequency noise on interacting superconducting qubits in a fixed coupling scheme. By properly choosing operating conditions, within the adiabatic framework the systems develops two decoupled subspaces. The subspace where a SWAP operation takes place turns out to be resilient to low frequency fluctuations. The possibility to encode a single qubit in a protected two-physical-qubit system subspace is briefly discussed.


Nature ◽  
2016 ◽  
Vol 532 (7597) ◽  
pp. 77-80 ◽  
Author(s):  
Masashi Hirose ◽  
Paola Cappellaro

Author(s):  
ZHANG Fu Gang

Abstract In this paper, we discuss quantum uncertainty relations of Tsallis relative $\alpha$ entropy coherence for a single qubit system based on three mutually unbiased bases. For $\alpha\in[\frac{1}{2},1)\cup(1,2]$, the upper and lower bounds of sums of coherence are obtained. However, the above results cannot be verified directly for any $\alpha\in(0,\frac{1}{2})$. Hence, we only consider the special case of $\alpha=\frac{1}{n+1}$, where $n$ is a positive integer, and we obtain the upper and lower bounds. By comparing the upper and lower bounds, we find that the upper bound is equal to the lower bound for the special $\alpha=\frac{1}{2}$, and the differences between the upper and the lower bounds will increase as $\alpha$ increases. Furthermore, we discuss the tendency of the sum of coherence, and find that it has the same tendency with respect to the different $\theta$ or $\varphi$, which is opposite to the uncertainty relations based on the R\'{e}nyi entropy and Tsallis entropy.


2009 ◽  
Vol 9 (5&6) ◽  
pp. 395-405
Author(s):  
J. Li ◽  
K. Jacobs

We derive the equations of motion describing the feedback control of quantum systems in the regime of ``good control", in which the control is sufficient to keep the system close to the desired state. One can view this regime as the quantum equivalent of the ``linearized" regime for feedback control of classical nonlinear systems. Strikingly, while the dynamics of a single qubit in this regime is indeed linear, that of all larger systems remains nonlinear, in contrast to the classical case. As a first application of these equations, we determine the steady-state performance of feedback protocols for a single qubit that use unbiased measurements.


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