Article

Wallraff, A. et al. Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics. Nature 431, 162-167

Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.
Nature (Impact Factor: 41.46). 10/2004; 431(7005):162-7. DOI: 10.1038/nature02851
Source: PubMed

ABSTRACT

The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics for several decades and has generated the field of cavity quantum electrodynamics. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.

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    • "The g 0 term is the conditional displacement interaction between the qubit and the oscillator. This Hamiltonian can be realized in various experimental platforms, such as cavity-or circuit-QED systems [51], electromechanical systems [23] [52], and spin-oscillator systems [48] [53]. "
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    ABSTRACT: We propose a scheme to generate macroscopic Schr\"{o}dinger's cat states in a quantum oscillator (electromagnetic field or mechanical resonator) coupled to a quantum bit (two-level system) via a conditional displacement mechanism. By driving the qubit monochromatically, the oscillation of the qubit state modifies the effective frequency of the driving force acting on the oscillator, and a resonant or near-resonant driving on the oscillator can be achieved. The displacement of the oscillator is then significantly enhanced due to the small detuning of the driving force and can exceed that of the zero-point fluctuation. This effect can be used to prepare quantum superpositions of macroscopically distinct coherent states in the oscillator. We present detailed studies on this state generation scheme in both closed and open system cases. This approach can be implemented in various experimental platforms, such as cavity- or circuit-QED systems, electromechanical systems, and spin-cantilever systems.
    Full-text · Article · Dec 2015
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    • "Here Γ vac is the free space spontaneous emission rate, σ 0 ∝ λ 2 is the resonant absorption cross section, Q, V , and F, are the cavity quality factor, volume, and finesse respectively, and A is the effective area of the cavity or guided mode that couples to the atom. The strongest coupling occurs on resonance, and thus much effort has been devoted to developing the largest possible Γ cav and Γ 1D through ultrahigh-Q , small-volume resonators [5] [9] [10] and through nanophotonic plasmonic [11] [12], metamaterial [13], and dielectric [8] [14] waveguides. "
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    ABSTRACT: We study the strong coupling between photons and atoms that can be achieved in an optical nanofiber geometry when the interaction is dispersive. While the Purcell enhancement factor for spontaneous emission into the guided mode does not reach the strong-coupling regime for individual atoms, one can obtain high cooperativity for ensembles of a few thousand atoms due to the tight confinement of the guided modes and constructive interference over the entire chain of trapped atoms. We calculate the dyadic Green's function, which determines the scattering of light by atoms in the presence of the fiber, and thus the phase shift and polarization rotation induced on the guided light by the trapped atoms. The Green's function is related to a full Heisenberg-Langevin treatment of the dispersive response of the quantized field to tensor polarizable atoms. We apply our formalism to quantum nondemolition (QND) measurement of the atoms via polarimetry. We study shot-noise-limited detection of atom number for atoms in a completely mixed spin state and the squeezing of projection noise for atoms in clock states. Compared with squeezing of atomic ensembles in free space, we capitalize on unique features that arise in the nanofiber geometry including anisotropy of both the intensity and polarization of the guided modes. We use a first principles stochastic master equation to model the squeezing as function of time in the presence of decoherence due to optical pumping. We find a peak metrological squeezing of ~5 dB is achievable with current technology for ~2500 atoms trapped 180 nm from the surface of a nanofiber with radius a=225 nm.
    Preview · Article · Sep 2015
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    • "Circuit quantum electrodynamics (cQED) [1] [2], based on the interactions of superconducting qubits with microwave light, is currently emerging as one of the most promising experimental platforms for quantum information processing [3] [4] and quantum optics experiments [5– 8]. In these superconducting circuits, Josephson junctions provide the necessary non-linearity for qubits, while low-loss microwave resonators are an essential component of quantum memories [9] [10] [11] [12], readout or entanglement buses [13] [14], and filtering [15] [16]. "
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    ABSTRACT: Experimental quantum information processing with superconducting circuits is rapidly advancing, driven by innovation in two classes of devices, one involving planar micro-fabricated (2D) resonators, and the other involving machined three-dimensional (3D) cavities. We demonstrate that circuit quantum electrodynamics (cQED), which is based on the interaction of low-loss resonators and qubits, can be implemented in a multilayer superconducting structure, which combines 2D and 3D advantages, hence its nickname "2.5." We employ standard micro-fabrication techniques to pattern each layer, and rely on a vacuum gap between the layers to store the electromagnetic energy. Planar superconducting qubits are lithographically defined as an aperture in a conducting boundary of multilayer resonators, rather than as a separate metallic structure on an insulating substrate. In order to demonstrate the potential of these design principles, we implemented an integrated, two-cavity-modes, one-transmon-qubit system for cQED experiments. The measured coherence times and coupling energies suggest that the 2.5D platform would be a promising base for integrated quantum information processing.
    Preview · Article · Sep 2015
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