Antiresonance Phase Shift in Strongly Coupled Cavity QED

Abstract

We investigate phase shifts in the strong coupling regime of single-atom cavity quantum electrodynamics (QED). On the light transmitted through the system, we observe a phase shift associated with an antiresonance and show that both its frequency and width depend solely on the atom, despite the strong coupling to the cavity. This shift is optically controllable and reaches 140 • -the largest ever reported for a single emitter. Our result offers a new technique for the characterization of complex integrated quantum circuits.The strongly coupled atom-cavity system plays a central role in research on fundamental quantum optics. Important achievements to date include the creation of single photon sources [1,2] and non-classical microwave states [3,4], single-atom squeezing [5], the observation of novel photon statistics [6][7][8] and the nondestructive detection of microwave and optical photons [9,10]. More complex interacting systems based on this basic element are now attracting much attention in quantum information and simulation. Recent achievements in this direction include the coupling of a single qubit to two cavities [11], the interaction of multiple qubits with a single cavity bus [12,13], and the exchange of quantum states between single qubits in remote cavities [14,15]. Integrated quantum circuits are promising candidates for on-chip quantum computation [16][17][18][19][20] and large strongly coupled networks have been proposed for simulating quantum phase transitions [21][22][23]. However, in such strongly interacting systems, the couplings no longer represent merely a perturbation of the subsystem dynamics, necessitating a holistic analysis of the coupled system. This makes the characterization of strongly coupled quantum circuits a challenging task [24,25].In this Letter, we propose a new technique for characterizing complex quantum circuits, which emerges from an analysis of the phase of light transmitted through a strongly coupled single-atom-cavity system. In particular, we report on the observation of an antiresonant phase shift caused by destructive interference between the coherent drive and the field radiated by the atom. The signature of the antiresonance is a large negative phase shift which depends solely on the atom, despite the strong coupling to the resonator. This is in sharp contrast to the normal modes [26,27], which depend on properties of both atom and cavity as well as the coupling strength [28]. Our measurement paves the way for individual components of strongly interacting quantum systems to be characterized via measurements performed only on the overall coupled system.Previous work on phase spectroscopy in cavity QED has focused on the so-called "bad-cavity" limit in which the cavity decay rate exceeds the coupling strength, κ > ∼ g, and only modest phase shifts were observed [29,30]. Phase changes due to strongly coupled atoms were seen in Ref. [31], but the antiresonance phase shift was not observed. The presence of a transmission dip at the atomic frequency (associated with th...

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“…Using the results from above gives the red curve in Figure 4.2c (reflection) and d (transmission). The transmission curve is in good agreement with the results of a recent publication [131]. In reflection, a phase shift of π is expected around zero detuning, meaning that the interaction mechanism works as intended.…”

Characterization of forced localization of disordered weakly coupled micromechanical resonators

“…However, it should be noted that the linear anti-resonance behavior is not very suitable as a sensing mechanism because tracking the anti-resonance introduces larger measurement errors compared to measuring frequency or amplitude shifts. The uncertainty/error of the anti-frequency is related to the phase noise 43 . The signal-to-noise ratio of the antiresonance is difficult to improve because the amplitude of the anti-resonance is smaller than that of the bias noise.…”

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“…Alternatively, the emitter can be placed in the focus of a deep parabolic lens, focussing and capturing almost all 4π solid angle of the emitted radiation [128]. Another approach again is to change the mode into which the emitter radiates, for example coupling it to a waveguide or an optical cavity, enabling large phase shifts [125,129] and change in reflection of up to 25% [130]. An interesting recent twist on the single quantum emitter coupling problem has been the creation of artificial superconducting atoms [131] which couple through one-dimensional superconducting channels, resulting in near-perfect extinction.…”