Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Phys Rev Lett. 2010 Nov 19;105(21):216803. doi: 10.1103/PhysRevLett.105.216803.
In many realizations of electron spin qubits the dominant source of decoherence is the fluctuating nuclear spin bath of the host material. The slowness of this bath lends itself to a promising mitigation strategy where the nuclear spin bath is prepared in a narrowed state with suppressed fluctuations. Here, this approach is realized for a two-electron spin qubit in a GaAs double quantum dot and a nearly tenfold increase in the inhomogeneous dephasing time T₂* is demonstrated. Between subsequent measurements, the bath is prepared by using the qubit as a feedback loop that first measures its nuclear environment by coherent precession, and then polarizes it depending on the final state. This procedure results in a stable fixed point at a nonzero polarization gradient between the two dots, which enables fast universal qubit control.
在许多电子自旋量子位的实现中，退相干的主要来源是宿主材料的核自旋涨落。这个涨落的缓慢为一种有前途的缓解策略提供了可能性，即在一个被抑制了涨落的狭窄状态下制备核自旋浴。在这里，这种方法在一个 GaAs 双量子点中的两个电子自旋量子位中得到了实现，并证明了非均匀退相时间 T₂*增加了近十倍。在随后的测量之间，通过使用量子位作为反馈环来制备浴，该反馈环首先通过相干进动来测量其核环境，然后根据最终状态对其进行极化。这个过程导致在两个点之间的非零极化梯度处达到一个稳定的固定点，这使得快速通用的量子位控制成为可能。
