Bath engineering of a fluorescing artificial atom with a photonic crystal

Abstract

We demonstrate how the dissipative interaction between a superconducting qubit and a microwave photonic crystal can be used for quantum bath engineering. The photonic crystal is created with a step-impedance transmission line which suppresses and enhances the quantum spectral density of states, influencing decay transitions of a transmon circuit. The qubit interacts with the transmission line indirectly via dispersive coupling to a cavity. We characterize the photonic crystal density of states from both the unitary and dissipative dynamics of the qubit. When the qubit is driven, it dissipates into the frequency dependent density of states of the photonic crystal. Our result is the deterministic preparation of qubit superposition states as the steady-state of coherent driving and dissipation near by the photonic crystal band edge, which we characterize with quantum state tomography. Our results highlight how the multimode environment from the photonic crystal forms a resource for quantum control. *

Quantum Thermodynamics and Optomechanics

“…Comme nous l'avons vu au chapitre 5, l'ingénierie du bain ouvre de nouvelles perspectives en thermodynamique quantique, permettant d'explorer les températures efficaces négatives [115] ou des cas où le bain fournit de la cohérence au système [67]. Mais cela rend la définition des quantités thermodynamiques comme la chaleur moins évidente.…”

“…As we saw in Chapter 5, bath engineering opens new perspectives in quantum thermodynamics, allowing to explore negative effective temperatures [115] or cases were the bath provides coherence to the system [67]. But this make the definition of thermodynamic quantities like heat less obvious.…”

“…In this chapter, we use an engineered bath to prepare the qubit in a coherent superpositions of energy eigenstates during the engine's first stroke. This bath consists of a pump, which is quasi-resonant with the qubit's frequency, and an electromagnetic reservoir whose mode density is engineered, for example, by using a cavity [93] or a photonic crystal [67]. We first derive the master equation describing the evolution of the qubit when coupled to this bath.…”

“…5.1b. Another option is to engineer the density of modes in the environment, for instance with a photonic crystal [67]. Furthermore, the angle θ ∈ [0, π] fixing the relaxation basis of the engineered bath can be tuned by playing on the pump detuning.…”

Assessment of weak-coupling approximations on a driven two-level system under dissipation

“…In this paper, we focus on the case where a single qubit is weakly driven by nearly resonant transverse fields and the interaction with a cold Ohmic bath produces effective dissipation rates that reach up to 10% of the bare qubit angular frequency. Experimentally, this scenario has been motivated by the recent progress in the implementation of tunable and engineered environments, for example, in circuit quantum electrodynamics (cQED) [78][79][80][81][82][83][84][85][86][87][88]. Note that another numerically exact and non-perturbative method has been proposed to capture more general initial system-bath states, including correlated ones [89].…”