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Register a new userBeyond Strong Coupling in a Massively Multimode Cavity
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The study of light-matter interaction has seen a resurgence in recent years, stimulated by highly controllable, precise, and modular experiments in cavity quantum electrodynamics (QED). The achievement of strong coupling, where the coupling between a single atom and fundamental cavity mode exceeds the decay rates, was a major milestone that opened the doors to a multitude of new investigations. Here we introduce multimode strong coupling (MMSC), where the coupling is comparable to the free spectral range (FSR) of the cavity, i.e. the rate at which a qubit can absorb a photon from the cavity is comparable to the round trip transit rate of a photon in the cavity. We realize, via the circuit QED architecture, the first experiment accessing the MMSC regime, and report remarkably widespread and structured resonance fluorescence, whose origin extends beyond cavity enhancement of sidebands. Our results capture complex multimode, multiphoton processes, and the emergence of ultranarrow linewidths. Beyond the novel phenomena presented here, MMSC opens a major new direction in the exploration of light-matter interactions.
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Demonstrating and exploiting the quantum nature of larger, more macroscopic mechanical objects would help us to directly investigate the limitations of quantum-based measurements and quantum information protocols, as well as test long standing questions about macroscopic quantum coherence. The field of cavity opto- and electro-mechanics, in which a mechanical oscillator is parametrically coupled to an electromagnetic resonance, provides a practical architecture for the manipulation and detection of motion at the quantum level. Reaching this quantum level requires strong coupling, interaction timescales between the two systems that are faster than the time it takes for energy to be dissipated. By incorporating a free-standing, flexible aluminum membrane into a lumped-element superconducting resonant cavity, we have increased the single photon coupling strength between radio-frequency mechanical motion and resonant microwave photons by more than two orders of magnitude beyond the current state-of-the-art. A parametric drive tone at the difference frequency between the two resonant systems dramatically increases the overall coupling strength. This has allowed us to completely enter the strong coupling regime. This is evidenced by a maximum normal mode splitting of nearly six bare cavity line-widths. Spectroscopic measurements of these dressed states are in excellent quantitative agreement with recent theoretical predictions. The basic architecture presented here provides a feasible path to ground-state cooling and subsequent coherent control and measurement of the quantum states of mechanical motion.
We study the cavity mode frequencies of a Fabry-Perot cavity containing two vibrating dielectric membranes. We derive the equations for the mode resonances and provide approximate analytical solutions for them as a function of the membrane positions, which act as an excellent approximation when the relative and center-of-mass position of the two membranes are much smaller than the cavity length. With these analytical solutions, one finds that extremely large optomechanical coupling of the membrane relative motion can be achieved in the limit of highly reflective membranes when the two membranes are placed very close to a resonance of the inner cavity formed by them. We also study the cavity finesse of the system and verify that, under the conditions of large coupling, it is not appreciably affected by the presence of the two membranes. The achievable large values of the ratio between the optomechanical coupling and the cavity decay rate, $g/kappa$, make this two-membrane system the simplest promising platform for implementing cavity optomechanics in the strong coupling regime.
Macroscopic mechanical objects and electromagnetic degrees of freedom couple to each other via radiation pressure. Optomechanical systems with sufficiently strong coupling are predicted to exhibit quantum effects and are a topic of considerable interest. Devices reaching this regime would offer new types of control of the quantum state of both light and matter and would provide a new arena in which to explore the boundary between quantum and classical physics. Experiments to date have achieved sufficient optomechanical coupling to laser-cool mechanical devices but have not yet reached the quantum regime. The outstanding technical challenge in this field is integrating sensitive micromechanical elements (which must be small, light, and flexible) into high finesse cavities (which are typically much more rigid and massive) without compromising the mechanical or optical properties of either. A second, and more fundamental, challenge is to read out the mechanical elements quantum state: displacement measurements (no matter how sensitive) cannot determine the energy eigenstate of an oscillator, and measurements which couple to quantities other than displacement have been difficult to realize. Here we present a novel optomechanical system which seems to resolve both these challenges. We demonstrate a cavity which is detuned by the motion of a thin dielectric membrane placed between two macroscopic, rigid, high-finesse mirrors. This approach segregates optical and mechanical functionality to physically distinct structures and avoids compromising either. It also allows for direct measurement of the square of the membranes displacement, and thus in principle the membranes energy eigenstate. We estimate it should be practical to use this scheme to observe quantum jumps of a mechanical system.
Cavity electro-(opto-)mechanics allows us to access not only single isolated but also multiple mechanical modes in a massive object. Here we develop a multi-mode electromechanical system in which a several membrane vibrational modes are coupled to a three-dimensional loop-gap superconducting microwave cavity. The tight confinement of the electric field across a mechanically-compliant narrow-gap capacitor brings the system into the quantum strong coupling regime under a red-sideband pump field. We demonstrate strong coupling between two mechanical modes, which is induced by two-tone parametric drives and mediated by a virtual photon in the cavity. The tunable inter-mechanical-mode coupling can be used to generate entanglement between the mechanical modes.
We present and analyze a method where parametric (two-photon) driving of a cavity is used to exponentially enhance the light-matter coupling in a generic cavity QED setup, with time-dependent control. Our method allows one to enhance weak-coupling systems, such that they enter the strong coupling regime (where the coupling exceeds dissipative rates) and even the ultra-strong coupling regime (where the coupling is comparable to the cavity frequency). As an example, we show how the scheme allows one to use a weak-coupling system to adiabatically prepare the highly entangled ground state of the ultra-strong coupling system. The resulting state could be used for remote entanglement applications.
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