Nondestructive measurement of the energy of microwave quanta using reactive nonlinearities

Vladimir B. Braginskii, Sergey P. Vyatchanin

Cyril Metzger, Alec L. Emser, Brendon C. Rose +1 more

We present experimental evidence of a thermally-driven amplitude-frequency nonlinearity in a thin-film quartz phononic crystal resonator at millikelvin temperatures. The nonlinear response arises from the coupling of the mechanical mode to an ensemble of microscopic two-level system defects driven out of equilibrium by a microwave drive. In contrast to the conventional Duffing oscillator, the observed nonlinearity exhibits a mixed reactive-dissipative character. Notably, the reactive effect can manifest as either a softening or hardening of the mechanical resonance, depending on the ratio of thermal to phonon energy. By combining the standard TLS theory with a thermal conductance model, the measured power-dependent response is quantitatively reproduced and readout-enhanced relaxation damping from off-resonant TLSs is identified as the primary mechanism limiting mechanical coherence. Within this framework, we delineate the conditions under which similar systems will realize this nonlinearity.

Yashika Aneja, Monika Thakran, Monika Yashika +3 more

Yashika Aneja, Monika Thakran, Asheesh Kumar Sharma +2 more

Kingshuk Adhikary, Darren W. Moore, Radim Filip

The ability of bosonic energy quanta to bunch together in an energy-conserving interaction is a fundamental feature of quantum harmonic oscillators. Linear systems together with measurement allow for the conditional concentration of energy quanta and, subsequently, breeding of the quantum states, but only with an exponentially decreasing success rate. Deterministic, energy-conserving and unconditional bunching however, requires nonlinearity. We investigate which nonlinear energy-conserving interactions deterministically combine bosons into high number states at the same frequency. We show that in order to do so it is advantageous to use nonlinear interactions involving highly saturable systems, such as qubits, as they preserve the hierarchical quantum non-Gaussian features and are also sufficiently robust against pure loss. Nonlinear bunching therefore demonstrates the advantage of a {\it qubit-inside} nonlinearity and opens new directions in the deterministic preparation, processing, and detection of quantum non-Gaussian states.

We propose and analyze an experimental scheme of quantum nondemolition detection of monophotonic and vacuum states in a superconductive toroidal cavity by means of Rydberg atoms. One of the key directions of modern physics is the following challenging problem of understanding the essence of the process of quantum measurement. Of special interest in this respect are experiments with individual quantum objects. Such applications as quantum computing, quantum cryptography and quantum teleportation, which have recently been attracting increasing attention [1], have their roots in this field. Quantum measurements and particularly experiments on the interaction of individual atoms and ions with the quantum field in a cavity are usually associated with the optical domain. With the development of the Rydberg atom technique, however, impressive results have been obtained in the microwave region [2]. This technique allows preparation and nondestructive (quantum non-demolition) repetitive measurements of Fock states with a small number of quanta in a high-Q superconductive cavity [3, 4]. In 1994 V.B.Braginsky and F.Ya.Khalili [5] proposed an elegant scheme employing Rydberg atoms which allowed nondestructive detection of vacuum and monophotonic states. The idea of the experiment is to use a cavity with a geometry such that the flying atom can interact twice with the field.