Superconducting qubit–oscillator circuit beyond the ultrastrong-coupling regime

By F. Yoshihara, T. Fuse, Sahel Ashhab, K. Kakuyanagi, S. Saito, K. Semba. Nature Physics, 2016

650 citations recorded by the source corpus.

A circuit that pairs a flux qubit with an LC oscillator via Josephson junctions pushes the coupling between light to matter to uncharted territory, with the potential for new applications in quantum technologies. The interaction between an atom and the electromagnetic field inside a cavity1,2,3,4,5,6 has played a crucial role in developing our understanding of light–matter interaction, and is central to various quantum technologies, including lasers and many quantum computing architectures. Superconducting qubits7,8 have allowed the realization of strong9,10 and ultrastrong11,12,13 coupling between artificial atoms and cavities. If the coupling strength g becomes as large as the atomic and cavity frequencies (Δ and ωo, respectively), the energy eigenstates including the ground state are predicted to be highly entangled14. There has been an ongoing debate15,16,17 over whether it is fundamentally possible to realize this regime in realistic physical systems. By inductively coupling a flux qubit and an LC oscillator via Josephson junctions, we have realized circuits with g/ωo ranging from 0.72 to 1.34 and g/Δ ≫ 1. Using spectroscopy measurements, we have observed unconventional transition spectra that are characteristic of this new regime. Our results provide a basis for ground-state-based entangled pair generation and open a new direction of research on strongly correlated light–matter states in circuit quantum electrodynamics.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/7f8dac3056c53b4d314a981469b9dd70bd2b0da6

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Citations in the corpus

Cavity Casimir-Polder Forces and Their Effects in Ground-State Chemical Reactivity (2018, background): “[55] Fumiki Yoshihara, Tomoko Fuse, Sahel Ashhab, Kosuke Kakuyanagi, Shiro Saito, and Kouichi Semba, “Superconducting Qubit–Oscillator Circuit beyond the Ultrastrong-Coupling Regime,” Nat.”
Continuous transition between weak and ultrastrong coupling through exceptional points in carbon nanotube microcavity exciton–polaritons (2018, methodology): “where NC (= 88 nm−1) is the number of carbon atoms per nanometre in a (6,5) nanotube, nc (= 1.”
Circuit quantum electrodynamics (2020, background): “These ideas were first realized in (Forn-Dı́az et al., 2010; Niemczyk et al., 2010) with g/ωq ∼ 0.1 and more recently with coupling strengths as large as g/ωq ∼ 1.34 (Yoshihara et al., 2016).”
Microwave photonics with superconducting quantum circuits (2017, methodology): “other SQC experiments that have reached the SQC regime [391, 393, 395, 397], including the only one to reach the DSC regime [395], have also used flux qubits, but coupled to a lumped-element LC oscillator instead.”
Semi-classical and quantum Rabi models: in celebration of 80 years (2016, methodology): “There are three basic reasons: (i) experiments have now been able to push into the ultrastrong (|ω| < 10g) [4, 5] and deep strong (|ω| < g) [6] coupling regimes in which the rotating-wave approximation and thus the Jaynes-Cummings model are not applicable; (ii) there are exciting prospects for novel”
Quantum Simulation Of The Quantum Rabi Model In A Trapped Ion (2017, background): “Recent experimental achievements have shown the accessibility to the ultrastrong coupling (USC) regime[15, 16] or even to the deep strong coupling (DSC) regime [17, 18], where the coupling strength is comparable to or larger than the mode frequency.”
Cavity magnonics (2021, background): “In the deep-strong coupling regime g/ωc & 1 (Bayer et al., 2017; Casanova et al., 2010; Yoshihara et al., 2016) the addition of just one photon may affect the system properties.”