Centre for Quantum Information &Quantum Control and Institute for Optical Sciences, Department of Physics, University of Toronto, 60 St. George St, Toronto, Ontario, M5S 1A7, Canada.
Canadian Institute For Advanced Research, 180 Dundas St. W., Toronto, Ontario, M5G 1Z8, Canada.
Sci Rep. 2016 Dec 15;6:38822. doi: 10.1038/srep38822.
A classical thermometer typically works by exchanging energy with the system being measured until it comes to equilibrium, at which point the readout is related to the final energy state of the thermometer. A recent paper noted that with a quantum thermometer consisting of a single spin/qubit, temperature discrimination is better achieved at finite times rather than once equilibration is essentially complete. Furthermore, preparing a qubit thermometer in a state with quantum coherence instead of an incoherent one improves its sensitivity to temperature differences. Implementing a recent proposal for efficiently emulating an arbitrary quantum channel, we use the quantum polarisation state of individual photons as models of "single-qubit thermometers" which evolve for a certain time in contact with a thermal bath. We investigate the optimal thermometer states for temperature discrimination, and the optimal interaction times, confirming that there is a broad regime where quantum coherence provides a significant improvement. We also discuss the more practical question of thermometers composed of a finite number of spins/qubits (greater than one), and characterize the performance of an adaptive protocol for making optimal use of all the qubits.
传统温度计通常通过与被测系统进行能量交换来工作，直到达到平衡状态，此时读数与温度计的最终能量状态有关。最近的一篇论文指出，对于由单个自旋/量子位组成的量子温度计，在有限的时间内实现温度区分比在基本达到平衡后要好。此外，通过将量子位温度计制备为具有量子相干性而不是非相干性的状态，可以提高其对温差的灵敏度。为了有效地模拟任意量子通道，我们使用单个光子的量子极化状态作为“单量子位温度计”的模型，这些温度计在与热浴接触一定时间后会发生演化。我们研究了用于温度区分的最佳温度计状态和最佳相互作用时间，证实了在一个广泛的范围内，量子相干性提供了显著的改进。我们还讨论了由有限数量的自旋/量子位（大于一）组成的温度计的更实际问题，并描述了一种自适应协议的性能，该协议可以最佳地利用所有量子位。
