Decoherence Control of Nitrogen-Vacancy Centers

Abstract

Quantum mechanical systems lose coherence through interacting with external environments-a process known as decoherence. Although decoherence is detrimental for most of the tasks in quantum information processing, a substantial degree of decoherence is crucial for boosting the efficiency of quantum processes, for example, in quantum biology and other open systems. The key to the success in simulating those open quantum systems is therefore the ability of controlling decoherence, instead of eliminating it. Motivated by simulating quantum open systems with Nitrogen-Vacancy centers, which has become an increasingly important platform for quantum information processing tasks, we developed a new set of steering pulse sequences for controlling various coherence times of Nitrogen-Vacancy centers; our method is based on a hybrid approach that exploits ingredients in both digital and analog quantum simulations to dynamically couple or decouple the system with the physical environment. Our numerical simulations, based on experimentally-feasible parameters, indicate that decoherence of Nitrogen-Vacancy centers can be controlled externally to a very large extend.

Figure 1

(a) Coherence vs evolution time with only nuclear spin noise, the variance of the random magnetic field is set to be $0.2$ Gauss. (b) Coherence time vs λ extracted from (a). (c)Evolution of population with time in real NV center, in which both nuclear spin noise and electron noise are considered, the dots are simulated points and the curves are fitted one. (d) Coherence time got from the fitting curve in (c) vs λ from 0 to 3, here the values of λ in the calculation are 0, 0.25, 0.5, 0.75, 1, 2, 3.

Figure 2

(a) Pulse sequence for two-level system, where $x$ means the microwave is applied along $x$ axis, the red bar is the idea $\pi$ pulse (i.e. the swap gate), blue rectangles mean the evolution of $H_S$, which in the numerical calculations we always set it to be 0 without losing generalization. (b) Coherence vs evolution time with different distance between two swap gate, the variance of the random magnetic field is set to be 0.2 $Gauss$. (c) Coherence time vs τ, which is defined in $\mu \mathrm{\Delta }t=\tau \lambda \mathrm{\Delta }t\mathrm{/2}$. (d) is the values of $|\tilde{f}(t,\omega {)|}^2$ which represent the noise spectrum. (e) The coherence vs time with different τ.

Figure 3

(a) Pulse sequences for the case applying the decoupling pulses in only one channel in three-level system, labels have the same meaning as Fig. 1. (b) Pulse sequences of the case that applying the decoupling pulses in two channel of the three-level system, where $MW1$ and $MW2$ mean the first and second microwave with different frequencies. (c)The coherence time vs τ(which is defined in $\mu \mathrm{\Delta }t=\tau \lambda \mathrm{\Delta }t\mathrm{/2}$), as τ increases, the coherence time $T_2^{12}$ increases and the other two coherence time remains almost the same, decrease or increase slightly. (d–f) show the coherence time between the three levels, with (d) is the $T_2^{12}$, (e) the $T_2^{13}$ and (f)$T_2^{23}$, in which τ ₁ and τ ₂ are defined in ${\mu }_{\mathrm{1(2)}}\mathrm{\Delta }t={\tau }_{\mathrm{1(2)}}\lambda \mathrm{\Delta }t\mathrm{/2}$, the blue region means the coherence time is small and the red ones is the case the coherence time increases sharply.