Victor Mukherjee
Weizmann Institute of Science
Victor Mukherjee is now working as a postdoctoral researcher at the Weizmann Institute of Science, Israel. Prior to his current position at the Weizmann Institute, he worked at the Scuola Normale Superiore in Pisa, Italy, and at the Ulm University in Germany. He did his PhD from IIT Kanpur, India. His research interests include quantum thermodynamics, quantum control, and quantum phase transitions.
Introduction: Precise probing of quantum systems is one of the keys to progress in diverse quantum technologies, including quantum thermometry and quantum information processing. Here we consider a thermometer modeled by a dynamically-controlled multilevel quantum system in contact with a bath. Dynamical control in the form of periodic modulation of the energy-level spacings of the quantum probe enables us to dramatically increase the accuracy of temperature estimation at low temperatures, by maximizing the relevant quantum Fisher information. As opposed to the diverging relative error at low temperatures obtained in conventional thermometers (Cf. green curve in the attached figure), periodic modulation of the probe enables high-precision thermometry close to the absolute zero, with a constant (temperature-independent) relative error bound (Cf. red and blue curves in the attached figure). Alternatively, such control may allow for high-precision measurement of a broad range of temperatures.
Methods: We quantify the accuracy of temperature estimation by the relevant quantum Fisher information (QFI). We apply periodic dynamical control on the multilevel quantum thermometer, and study the dynamics of the thermometer using Floquet method. The periodic modulation modifies the steady state of the dynamically controlled quantum thermometer (DCQT), which further enables us to control the QFI in the temperature ranges of interest.
Results: Application of dynamical control increases the QFI, and consequently reduces the relative error of temperature estimation significantly, for a broad range of bath spectra (Cf. inset of the attached figure). This enables us to perform high-precision thermometry for low temperatures, as well as increase the accuracy of temperature estimation for a broad range of bath temperatures.
Discussion: We have shown that by subjecting a thermometer to an appropriate dynamical control, we may increase its accuracy for measuring a chosen range of temperatures. The advantage of our DCQT becomes especially apparent at low temperatures, where its accuracy in measuring the bath temperature, quantified by the QFI, is dramatically higher than that of its unmodulated counterpart. Namely, our dynamical control scheme allows us to measure low temperatures with high precision for a broad variety of bath spectra, under appropriate conditions.
