Power of Pausing: Advancing Understanding of Thermalization in Experimental Quantum Annealers
Power of Pausing: Advancing Understanding of Thermalization in Experimental Quantum Annealers
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DOI：
10.1103/physrevapplied.11.044083
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发表时间：
2019-04-25
影响因子：
4.6
通讯作者：
Rieffel, Eleanor G.
中科院分区：
文献类型：
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作者：
Marshall, Jeffrey;Venturelli, Davide;Rieffel, Eleanor G.
我们研究了当前一代量子退火硬件（D-Wave 2000 Q）的替代退火时间表，其中包括使用中间暂停的正向和反向退火。这项工作为这些设备（以及一般的量子设备）的内部工作提供了新的见解，特别是热效应如何控制系统动力学。我们表明，通过退火中途暂停可以导致输出分布的戏剧性变化，我们提供的证据表明热化确实发生在这样的暂停。我们表明，在最小间隙后不久暂停系统在一个狭窄的区域，成功地找到基态的问题哈密顿量的概率可以增加一个数量级。我们将这种效应与松弛（即，热化）在最小能隙附近区域发生非绝热和热激发之后。对于一组高达500个量子比特的大规模问题，我们证明了从退火机返回的分布非常接近问题哈密顿量的（经典）玻尔兹曼分布，尽管温度至少比退火机的（有效）温度高1.5倍。此外，我们发现，较大的问题更有可能热化到一个经典的玻尔兹曼分布。
We investigate alternative annealing schedules on the current generation of quantum-annealing hardware (the D-Wave 2000Q), which includes the use of forward and reverse annealing with an intermediate pause. This work provides new insights into the inner workings of these devices (and quantum devices in general), particularly into how thermal effects govern the system dynamics. We show that a pause midway through the anneal can cause a dramatic change in the output distribution, and we provide evidence suggesting thermalization is indeed occurring during such a pause. We demonstrate that upon pausing the system in a narrow region shortly after the minimum gap, the probability of successfully finding the ground state of the problem Hamiltonian can be increased over an order of magnitude. We relate this effect to relaxation (i.e., thermalization) after diabatic and thermal excitations that occur in the region near to the minimum gap. For a set of large-scale problems of up to 500 qubits, we demonstrate that the distribution returned from the annealer very closely matches a (classical) Boltzmann distribution of the problem Hamiltonian, albeit one with a temperature at least 1.5 times higher than the (effective) temperature of the annealer. Moreover, we show that larger problems are more likely to thermalize to a classical Boltzmann distribution.