Salari Sehdaran Fahimeh, Bina Matteo, Benedetti Claudia, Paris Matteo G A
Faculty of Physics, Shahid Bahonar University of Kerman, Kerman 76169-14111, Iran.
Quantum Technology Lab, Dipartimento di Fisica "Aldo Pontremoli", Università di Milano, I-20133 Milano, Italy.
Entropy (Basel). 2019 May 12;21(5):486. doi: 10.3390/e21050486.
It is often the case that the environment of a quantum system may be described as a bath of oscillators with an ohmic density of states. In turn, the precise characterization of these classes of environments is a crucial tool to engineer decoherence or to tailor quantum information protocols. Recently, the use of quantum probes in characterizing ohmic environments at zero-temperature has been discussed, showing that a single qubit provides precise estimation of the cutoff frequency. On the other hand, thermal noise often spoil quantum probing schemes, and for this reason we here extend the analysis to a complex system at thermal equilibrium. In particular, we discuss the interplay between thermal fluctuations and time evolution in determining the precision attainable by quantum probes. Our results show that the presence of thermal fluctuations degrades the precision for low values of the cutoff frequency, i.e., values of the order ω c ≲ T (in natural units). For larger values of ω c , decoherence is mostly due to the structure of environment, rather than thermal fluctuations, such that quantum probing by a single qubit is still an effective estimation procedure.
通常情况下，量子系统的环境可以描述为具有欧姆态密度的振子浴。反过来，对这类环境的精确表征是设计退相干或定制量子信息协议的关键工具。最近，人们讨论了使用量子探针来表征零温度下的欧姆环境，结果表明单个量子比特能够精确估计截止频率。另一方面，热噪声常常会破坏量子探测方案，因此我们在此将分析扩展到处于热平衡的复杂系统。具体而言，我们讨论了热涨落与时间演化之间的相互作用，以确定量子探针可达到的精度。我们的结果表明，对于截止频率的低值，即ωc≲T（自然单位）量级的值，热涨落的存在会降低精度。对于较大的ωc值，退相干主要是由于环境结构，而非热涨落，因此单个量子比特的量子探测仍然是一种有效的估计方法。
