Dynamical decoupling of qubits in a spin bath under periodic quantum control
Dynamical decoupling of qubits in a spin bath under periodic quantum control
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DOI：
10.1103/physreva.82.062120
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发表时间：
2010-12
影响因子：
2.9
通讯作者：
Jun-Ting Kao;Jo-Tzu Hung;Pochung Chen;C. Mou
中科院分区：
文献类型：
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作者：
Jun-Ting Kao;Jo-Tzu Hung;Pochung Chen;C. Mou
研究了在动态去耦合(DD)方案下，与相互作用的量子自旋1/2链耦合的单自旋和双自旋量子比特保持相干和纠缠的可行性。通过对在量子比特变去相干之前可以以T为周期周期性施加的计算脉冲的数量进行计数来检查性能，同时在每个周期内施加相同的去耦合脉冲序列。通过考虑由磁场控制的混合方向和有限宽度的脉冲，结果表明，脉宽积累降低了脉冲数目较多的序列的性能，而实际可行的磁场仅限于每个周期内具有少于10个去耦合脉冲的序列。此外，在每个周期T内，精确的非平凡脉冲序列可以逐渐地抑制量子位浴耦合到O(T{sup N+1})，当N=1、2、3时，最小脉冲数为4、7和12。当应用于所有量子比特时，这些序列被证明既保持纠缠又保持相干。基于含时密度矩阵重整化，我们的数值结果表明，对于实验室中可用的中等磁场(10-40T)，当每个周期中的脉冲数目为4或7个时，总体性能最佳。我们的结果为在固态中保持自旋量子比特的相干性和纠缠提供了有用的指导。
We investigate the feasibility for the preservation of coherence and entanglement of one- and two-spin qubits coupled to an interacting quantum spin-1/2 chain within the dynamical decoupling (DD) scheme. The performance is examined by counting the number of computing pulses that can be applied periodically with periods of T before qubits become decoherent, while an identical decoupling pulse sequence is applied within each cycle. By considering pulses with mixed directions and finite width controlled by magnetic fields, it is shown that pulse-width accumulation degrades the performance of sequences with larger numbers of pulses and that feasible magnetic fields in practice restrict consideration to sequences with few than 10 decoupling pulses within each cycle. Furthermore, within each cycle T, exact nontrivial pulse sequences are found to suppress the qubit-bath coupling to O(T{sup N+1}) progressively with the minimum number of pulses being 4, 7, and 12 for N=1,2,3. These sequences, when applied to all qubits, are shown to preserve both the entanglement and coherence. Based on time-dependent density matrix renormalization, our numerical results show that for modest magnetic fields (10-40 T) available in laboratories, the overall performance is optimized when the number of pulses in each cycle is 4 or 7 withmore » pulse directions alternating between x and z. Our results provide useful guides for the preservation of coherence and entanglement of spin qubits in the solid state.« less