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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Available from: David Schuster, Jun 03, 2014
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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.
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    • "MHz [25– 27]. The cQED architecture has been used to achieve strong coupling between microwave frequency photons and a superconducting qubit [25]. More recently, a variety of quantum dot devices (GaAs, carbon nanotubes, InAs nanowires, etched graphene) have been integrated with microwave cavities [26] [27] [28] [29]. "
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    ABSTRACT: Emission linewidth is an important figure of merit for masers and lasers. We recently demonstrated a semiconductor double quantum dot (DQD) micromaser where photons are generated through single electron tunneling events. Charge noise directly couples to the DQD energy levels, resulting in a maser linewidth that is more than 100 times larger than the Schawlow-Townes prediction. Here we demonstrate a linewidth narrowing of more than a factor 10 by locking the DQD emission to a coherent tone that is injected to the input port of the cavity. We measure the injection locking range as a function of cavity input power and show that it is in agreement with the Adler equation. The position and amplitude of distortion sidebands that appear outside of the injection locking range are quantitatively examined. Our results show that this unconventional maser, which is impacted by strong charge noise and electron-phonon coupling, is well described by standard laser models.
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    • "When system B is a photon field andˆH B is proportional to the number of photons in the field, thenˆH AB describes the weak probing of the population difference of an ensemble of two-level atoms with far-detuned light [37, 51– 60], or dispersive coupling between a microwave cavity and a superconducting qubit [61] [62] [63]. We will explore this specific case shortly, however, for now we keepˆH B completely general. "
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    ABSTRACT: Quantum-enhanced metrology can be achieved by entangling a probe with an auxiliary system, passing the probe through an interferometer, and subsequently making measurements on both the probe and auxiliary system. Conceptually, this corresponds to performing metrology with the purification of a (mixed) probe state. We demonstrate via the quantum Fisher information how to design mixed states whose purifications are an excellent metrological resource. In particular, we give examples of mixed states with purifications that allow (near) Heisenberg-limited metrology, and provide example entangling Hamiltonians that can generate these states. Finally, we present the optimal measurement and parameter-estimation procedure required to realize these sensitivities (i.e. that saturate the quantum Cram\'er-Rao bound). Since pure states of comparable metrological usefulness are typically challenging to generate, it may prove easier to use this approach of entanglement and measurement of an auxiliary system. An example where this may be the case is atom interferometry, where entanglement with optical systems is potentially easier to engineer than the atomic interactions required to produce nonclassical atomic states.
    Physical Review A 07/2015; 92(3). DOI:10.1103/PhysRevA.92.032317 · 2.81 Impact Factor
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