Spontaneous emission of Schrödinger cats in a waveguide at ultrastrong coupling

Gheeraert, Nicolas; Bera, Soumya; Florens, Serge

doi:10.1088/1367-2630/aa5dea

Cited by 26 publications

(32 citation statements)

References 48 publications

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“…The blue shaded area represents the theoretical expectation for ΓT, within a confidence interval given by the error in the capacitances in Table I. finite environment has the same influence on the qubit as a truly macroscopic bath. The further possibility to tune the coupling to the environment in-situ, demonstrated by a 50% flux-modulation of the qubit linewidth, opens the way to controlled quantum optics experiments where many-body effects are fully-developped 16,17,19,20,56,57 , as well as more advanced environmental engineering for superconducting qubits 25 .…”

Section: Resultsmentioning

confidence: 99%

A tunable Josephson platform to explore many-body quantum optics in circuit-QED

et al. 2019

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The interaction between light and matter remains a central topic in modern physics despite decades of intensive research. Coupling an isolated emitter to a single mode of the electromagnetic field is now routinely achieved in the laboratory 1 , and standard quantum optics provides a complete toolbox for describing such a setup. Current efforts aim to go further and explore the coherent dynamics of systems containing an emitter coupled to several electromagnetic degrees of freedom 2-6 . Recently, ultrastrong coupling to a transmission line has been achieved where the emitter resonance broadens to a significant fraction of its frequency, and hybridizes with a continuum of electromagnetic (EM) modes 7,8 . In this work we gain significantly improved control over this regime. We do so by combining the simplicity and robustness of a transmon qubit and a bespoke EM environment 6,9,10 with a high density of discrete modes, hosted inside a superconducting metamaterial 11 . This produces a unique device in which the hybridisation between the qubit and many modes (up to ten in the current device) of its environment can be monitored directly. Moreover the frequency and broadening of the qubit resonance can be tuned independently of each other in situ. We experimentally demonstrate that our device combines this tunability with ultrastrong coupling 12-15 and a qubit nonlinearity comparable to the other relevant energy scales in the system. We also develop a quantitative theoretical description that does not contain any phenomenological parameters and that accurately takes into account vacuum fluctuations of our large scale quantum circuit in the regime of ultrastrong coupling and intermediate non-linearity. The demonstration of this new platform combined with a quantitative modelling brings closer the prospect of experimentally studying many-body effects in quantum optics. A limitation of the current device is the intermediate nonlinearity of the qubit. Pushing it further will induce fully developed many-body effects, such as a giant Lamb shift 16 or nonclassical states of multimode optical fields 17-20 . Observing such effects would establish interesting links between quantum optics and the physics of quantum impurities 21,22 . IntroductionDue to strong interactions between elementary constituants, correlated solids 23 and trapped cold atoms 24 host fascinating many-body phenomena. Attempts to produce similar effects in purely optical systems are hampered by the obvious fact that photons do not naturally interact with each other. If this obstacle can be overcome, there is the tantalizing prospect of probing the many-body problem using the contents of the quantum optics toolbox, such as single photon sources and detectors, high-order correlations in time-resolved measurements, entanglement measures, and phase space tomographies to name a few.One route to building a many-body quantum optical system is to rely on arrays of strongly non-linear cavities or resonators 22,25,26 , but minimising disorder in such architectures is a fo...

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Section: Resultsmentioning

confidence: 99%

A tunable Josephson platform to explore many-body quantum optics in circuit-QED

et al. 2019

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“…In ultra-strong wQED, many-body phenomena are expected to occur that have no counterpart in standard quantum optics [2,3] or in low-coupling superconduct-ing transmission lines [20][21][22][23][24][25][26]. A non-exhaustive list of theoretical predictions includes giant Lamb shifts [27][28][29][30][31], single-photon down-conversion [32,33], non-RWA transmission lineshapes [28,34,35], multi-mode entanglement [36][37][38], and non-classical emission [39]. The key element in all of the novel many-body phenomena in ultra-strong wQED is that the number of excitations is no longer conserved because the rotating-wave approximation is not legitimate anymore.…”

Section: Introductionmentioning

confidence: 99%

Particle production in ultrastrong-coupling waveguide QED

et al. 2018

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Understanding large-scale interacting quantum matter requires dealing with the huge number of quanta that are produced by scattering even a few particles against a complex quantum object. Prominent examples are found from high energy cosmic ray showers, to the optical or electrical driving of degenerate Fermi gases. We tackle this challenge in the context of many-body quantum optics, as motivated by the recent developments of circuit quantum electrodynamics at ultrastrong coupling. The issue of particle production is addressed quantitatively with a simple yet powerful concept rooted in the quantum superposition principle of multimode coherent states. This key idea is illustrated by the study of multi-photon emission from a single two-level artificial atom coupled to a high impedance waveguide, driven by a nearly-monochromatic coherent tone. We find surprisingly that the off-resonant inelastic emission lineshape is dominated by broadband particle production, due to the large phase space associated with contributions that do not conserve the number of excitations. Such frequency conversion processes produce striking signatures in time correlation measurements, which can be tested experimentally in quantum waveguides. These ideas open new directions for the simulation of a variety of physical systems, from polaron dynamics in solids to complex superconducting quantum architectures. arXiv:1802.01665v3 [cond-mat.mes-hall]

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“…In this standard model, to be described in further detail below, a single quantized spin interacts with a continuum of bosonic modes, with a spectrum of coupling constants that vanishes with a power law s < 1 at low energy. For this purpose, we shall use a combination of two numerically exact wave-function-based methods for quantum impurity models: a variational matrix-product-state approach (VMPS) [8][9][10][11] and the coherent-state expansion (CSE) [12][13][14][15]. VMPS is an abbreviation for the variational matrix-product-state (MPS) formulation of the density matrix renormalization group (DMRG), which has been established as a very powerful and flexible technique, also in the context of bosonic impurity models [11,16,17], and will be used as a reference.…”

Section: Introductionmentioning

confidence: 99%

Anatomy of quantum critical wave functions in dissipative impurity problems

et al. 2017

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Quantum phase transitions reflect singular changes taking place in a many-body ground state; however, computing and analyzing large-scale critical wave functions constitutes a formidable challenge. Physical insights into the sub-Ohmic spin-boson model are provided by the coherent-state expansion (CSE), which represents the wave function by a linear combination of classically displaced configurations. We find that the distribution of low-energy displacements displays an emergent symmetry in the absence of spontaneous symmetry breaking while experiencing strong fluctuations of the order parameter near the quantum critical point. Quantum criticality provides two strong fingerprints in critical low-energy modes: an algebraic decay of the average displacement and a constant universal average squeezing amplitude. These observations, confirmed by extensive variational matrix-product-state (VMPS) simulations and field theory arguments, offer precious clues into the microscopics of critical many-body states in quantum impurity models.

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Spontaneous emission of Schrödinger cats in a waveguide at ultrastrong coupling

Cited by 26 publications

References 48 publications

A tunable Josephson platform to explore many-body quantum optics in circuit-QED

A tunable Josephson platform to explore many-body quantum optics in circuit-QED

Particle production in ultrastrong-coupling waveguide QED

Anatomy of quantum critical wave functions in dissipative impurity problems

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