My research explores the scientific frontiers in quantum technologies, ranging from exploring the nature of time and clocks in quantum theory to the quantum mechanics of cooling and high-precision tests of gravity in the quantum regime. Several of these research directions are driven by the guiding principles of quantum optics, in particular, the quantum mechanics of sources and resonant detectors for quantized radiation fields. They find broader applications to characterize effective quantum field theories at low energies. If gravity has a quantum description, we expect that gravitational radiation must also have quantum characteristics. My recent works have explored feasible tests of violations of the coherent state hypothesis for gravitational radiation, as a probe for its quantum character in low-energy experiments. Here, inferences are made based on statistical fluctuations in observable measurement records, and we identify experimental scenarios where the observable statistics are best described by applying quantum theory to gravitational radiation.
Sources of quantized radiation fields are also of great interest. Time-varying, electrically-charged dipole moments emit electromagnetic radiation, while time-varying mass quadrupole moments (such as binary black hole merger events) produce gravitational waves. It is a fundamental principle of quantum optics that good emitters are also good detectors, which allows for a lot of synergies in my thoughts and research. The simplest of detectors for light must have a nonzero transition dipole moment, while the simplest of gravitational wave detectors are mass quadrupoles.
An interesting avenue where characterizing sources of quantum light is important is that of atomic clocks. Atomic clocks are also quantum mechanical systems. Therefore, the very act of measuring time would induce a back-reaction on the dynamics of the clock itself. This suggests a fundamental limitation to how good a clock can be, in addition to the limitations imposed by the principles of thermodynamics. Towards addressing this challenging question, my recent works have explored the fundamental limits quantum measurements impose on the precision and accuracy of (artificial) atomic clocks. Compared to real atomic clocks, artificial atomic clocks can tick at much slower timescales, allowing for the study of their undersampled regime where quantum fluctuations are not averaged out. Ideas from stochastic thermodynamics and statistical mechanics, such as fluctuation theorems and the large deviation principle, find important applications to characterize this regime.
Almost all practical quantum technologies, including sources and detectors for quantized radiation fields, often require very low temperatures to operate, and achieving very low temperatures on demand is a challenging task. Quantum mechanics could offer resolutions to this problem through enhanced cooling strategies that outperform their classical counterparts, and I am very motivated to explore such novel cooling schemes. Some of the cyclic cooling strategies I have proposed make use of superconducting quantum condensates. Quantum absorption cooling using tunable quantum control elements, such as quantum thermoelectrics, is another idea I have explored. They broadly fall under the umbrella of quantum thermodynamic control schemes, where the objective is to achieve control over thermodynamic variables across a quantum circuit, while respecting the laws of thermodynamics. My recent works also explore fundamental limits to parametric feedback cooling in the quantum regime, whose classical counterpart is widely used.
The creation of fire at will was probably the first ever technological milestone for our species. Almost all civilizations around the world treated fire with respect, learned and benefited from it. Eons down the line, we are still trying to figure out some aspects of how to control and manipulate fire (or thermal fluctuations) to our complete satisfaction. If learning quantum mechanics can be considered in a similar spirit as our most recent technological milestone, it may appear that it could still be a while before we control and manipulate the quantum (fluctuations) to our complete satisfaction. However, just as was the case with fire, we can continuously learn and benefit from it, and that is indeed our goal here.