We report observations of transitions between excited states in the Jaynes-Cummings ladder of circuit quantum electrodynamics with electron spins (spin circuit QED). We show that unexplained features in recent experimental work correspond to such transitions and present an input-output framework that includes these effects. In new experiments, we first reproduce previous observations and then reveal both excited-state transitions and multiphoton transitions by increasing the probe power and using two-tone spectroscopy. This ability to probe the Jaynes-Cummings ladder is enabled by improvements in the coupling-to-decoherence ratio, and shows an increase in the maturity of spin circuit QED as an interesting platform for studying quantum phenomena.
We report observations of transitions between excited states in the Jaynes-Cummings ladder of circuit quantum electrodynamics with electron spins (spin circuit QED). We show that unexplained features in recent experimental work correspond to such transitions and present an input-output framework that includes these effects. In new experiments, we first reproduce previous observations and then reveal both excited-state transitions and multiphoton transitions by increasing the probe power and using two-tone spectroscopy. This ability to probe the Jaynes-Cummings ladder is enabled by improvements in the coupling-to-decoherence ratio, and shows an increase in the maturity of spin circuit QED as an interesting platform for studying quantum phenomena.
The response of the Jaynes--Cummings (JC) model to strong driving has been examined previously, but the origin of intriguing features near emitter--cavity resonance remains poorly understood because of the large background in conventional transmission spectroscopy. Here we introduce a spectroscopic approach for circuit quantum electrodynamics that combines strong cavity driving with quantum-nondemolition qubit readout. Separating the drive and readout substantially enhances the measurement sensitivity as compared with conventional cavity-transmission spectroscopy. With this technique, we identify the near-resonant features as multiphoton transitions between emitter--photon dressed states of the same parity, and resolve transitions between dressed states of opposite parity. Away from resonance, we also observe selective enhancement and suppression of multiphoton transitions, together with transitions involving the second excited state of the anharmonic qubit. Our approach opens a route to resolving the rich transition structure of the JC ladder and probing strongly driven light--matter interactions.
Chapter 4 is the first preparatory one toward elaboration on quantum many-body physics—it deals with circuit quantum electrodynamics (QED), i.e. systems of coupled Josephson qubits in macro-cavities, which correspond to coupled Jaynes–Cummings (JC) models. The chapter starts with the discussion of the rich physics of Josephson qubits, and then focuses on the (generalized) JC nonlinearity and spectrum revisited in the light of circuit QED. Finally, control and transfer of quantum information in circuit QED is discussed.
The Jaynes–Cummings (JC) model has been the theoretical workhorse for understanding cavity quantum electrodynamics (QED) and for exploring multiphoton effects caused by the quantization of light. Today, it is an indispensable tool used to describe a variety of quantum optical systems, including semiconductor quantum-dot (QD) cavities, atoms in cavities, and superconducting circuits. Unfortunately, dissipation in many cavity-QED systems, especially QD structures, can strongly inhibit any direct spectral features of higher lying photon states and their spectral anharmonicities. In this work, we introduce a strategy to directly access and probe these multiphoton states and show that they can be directly observed even in the presence of a significant amount of dissipation. Our excitation scheme employs off-resonant excitation of a coupled QD cavity system using a nonlinear coherent drive, and the computed fluorescence spectra demonstrate the feasibility of the direct spectroscopic observation of higher rungs of the JC ladder using realistic QD cavity systems.
Light and matter can be unified under the strong coupling regime, creating superpositions of both, called dressed states or polaritons. After initially being demonstrated in bulk semiconductors and atomic systems ,strong coupling phenomena have been realized in solid state optical microcavities. They form an essential ingredient in the exciting physics spanning from many-body quantum coherence phenomena, like Bose-Einstein condensation and superfluidity, to cavity quantum electrodynamics (cQED). A widely used approach within cQED is the Jaynes-Cummings (JC) model that describes the interaction of a single fermionic two-level system with a single bosonic photon mode. For a photon number larger than one, known as quantum strong coupling (QSC), a significant anharmonicity is predicted for the ladder-like spectrum of dressed states. For optical transitions in semiconductor nanostructures, first signatures of the quantum strong coupling were recently published. In our latest report we applied advanced coherent nonlinear spectroscopy to explore a strongly coupled exciton-cavity system. Specifically, we measured and simulated its four-wave mixing (FWM) response, granting direct access to the first two rungs of the JC ladder. This paper summarizes the main results of Ref. 15 and adds FWM experiments obtained on a micropillar cavity in which a doublet of quantum dot (QD) excitons interacts with the cavity mode in the limit of weak to strong coupling.
Ultrastrong-coupling between two-level systems and radiation is important for both fundamental and applied quantum electrodynamics (QED). Such regimes are identified by the breakdown of the rotating-wave approximation, which applied to the quantum Rabi model (QRM) yields the apparently less fundamental Jaynes-Cummings model (JCM). We show that when truncating the material system to two levels, each gauge gives a different description whose predictions vary significantly for ultrastrong-coupling. QRMs are obtained through specific gauge choices, but so too is a JCM without needing the rotating-wave approximation. Analysing a circuit QED setup, we find that this JCM provides more accurate predictions than the QRM for the ground state, and often for the first excited state as well. Thus, Jaynes-Cummings physics is not restricted to light-matter coupling below the ultrastrong limit. Among the many implications is that the system's ground state is not necessarily highly entangled, which is usually considered a hallmark of ultrastrong-coupling.
Abstract The Jaynes‐Cummings model describes the coupling between photons and a single two‐level atom in a simplified representation of light‐matter interactions. In circuit QED, this model is implemented by combining microwave resonators and superconducting qubits on a microchip with unprecedented experimental control. Arranging qubits and resonators in the form of a lattice realizes a new kind of Hubbard model, the Jaynes‐Cummings‐Hubbard model, in which the elementary excitations are polariton quasi‐particles. Due to the genuine openness of photonic systems, circuit QED lattices offer the possibility to study the intricate interplay of collective behavior, strong correlations and non‐equilibrium physics. Thus, turning circuit QED into an architecture for quantum simulation, i.e., using a well‐controlled system to mimic the intricate quantum behavior of another system too daunting for a theorist to tackle head‐on, is an exciting idea which has served as theorists’ playground for a while and is now also starting to catch on in experiments. This review gives a summary of the most recent theoretical proposals and experimental efforts.