Preparation of subradiant states using local qubit control in circuit QED

Filipp, Stefan; Loo, Arjan F. van; Baur, M.; Steffen, L.; Wallraff, Andreas

doi:10.1103/physreva.84.061805

Cited by 47 publications

(55 citation statements)

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“…From a quantum-information perspective, subradiant states are interesting because they span a decoherence-free subspace [16][17][18]. A subradiant state of two superconducting qubits coupled to a cavity has recently been prepared [19].Here, we generate collective states of two ions coupled to an optical cavity and use a state that maximizes the coupling rate to improve ion-photon quantum information transfer. Our system is described by the Tavis-Cummings Hamiltonian [21], the interaction term of which is…”

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confidence: 99%

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Enhanced Quantum Interface with Collective Ion-Cavity Coupling

et al. 2015

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We prepare a maximally entangled state of two ions and couple both ions to the mode of an optical cavity. The phase of the entangled state determines the collective interaction of the ions with the cavity mode, that is, whether the emission of a single photon into the cavity is suppressed or enhanced. By adjusting this phase, we tune the ion-cavity system from sub-to superradiance. We then encode a single qubit in the two-ion superradiant state and show that this encoding enhances the transfer of quantum information onto a photon.Sub-and superradiance are fundamental effects in quantum optics arising in systems that are symmetric under the interchange of any pair of particles [1][2][3]. Superradiance has been widely studied in many-atom systems, in which effects such as a phase transition [4,5] and narrow-linewidth lasing [6] have recently been observed. For few-atom systems, each atom's state and position can be precisely controlled, and thus collective emission effects such as Rydberg blockade [7] and the Lamb shift [8] can be tailored. In a pioneering experiment using two trapped ions, variation of the ions' separation allowed both sub-and superradiance to be observed, with the excited-state lifetime extended or reduced by up to 1.5% [9]. The contrast was limited because spontaneous emission from the ions was not indistinguishable, as the ions' separation was on the order of the wavelength of the emitted radiation. This limitation can be overcome by observing preferential emission into a single mode, such as the mode defined by incident radiation [1] or by an optical cavity. In a cavity setting, indistinguishability is guaranteed when the emitters are equally coupled to the mode, even if they are spatially separated. Subradiance corresponds to a suppressed interaction of the joint state of the emitters with the cavity mode, while for the superradiant state, the interaction is enhanced.In the context of quantum networks [10,11], superradiance can improve a quantum interface when one logical qubit is encoded across N physical qubits. In the DLCZ protocol for heralded remote entanglement, efficient retrieval of stored photons is based on superradiance [12,13]. Superradiance can also improve the performance of a deterministic, cavity-based interface, which enables the direct transmission of quantum information between network nodes [14]. If a qubit is encoded in the state.. ↓ N , the coupling rate to the cavity is enhanced from the single-qubit rate g to the effective rate g √ N , relaxing the technical requirements for strong coupling between light and matter [15]. This state corresponds to the first step in the superradiant cascade described by Dicke [1]. In contrast, subradiant states are antisymmetrized, resulting in suppressed emission. From a quantum-information perspective, subradiant states are interesting because they span a decoherence-free subspace [16][17][18]. A subradiant state of two superconducting qubits coupled to a cavity has recently been prepared [19].Here, we generate collective states of tw...

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Enhanced Quantum Interface with Collective Ion-Cavity Coupling

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“…The third term in Eq. (12) represents the Purcell effect at the damping rate κλ 2 which can be reduced by operating the qubits in the dispersive regime [16,18,23], while the fourth term contains both the measurement-induced dephasing …”

Section: System: Hamiltonian and Stochastic Master Equationmentioning

confidence: 99%

“…Circuit QED system [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] in which superconducting qubits based on Josephson junctions are coupled to a high-Q microwave transmission line resonator acting as a quantum bus has been demonstrated to be a promising solid-state quantum computing architecture. Due to the great controllability of the superconducting qubits and microwaves in the circuit system, the circuit QED system, a solid-state analogy of quantum optics cavity QED, also has excellent potential as a platform for quantum control-especially quantum feedback control-experiments [27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Generation and stabilization of a three-qubit entangledWstate in circuit QED via quantum feedback control

Huang

Goan

et al. 2013

Phys. Rev. A

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Circuit cavity quantum electrodynamics (QED) is proving to be a powerful platform to implement quantum feedback control schemes due to the ability to control superconducting qubits and microwaves in a circuit.Here, we present a simple and promising quantum feedback control scheme for deterministic generation and stabilization of a three-qubit W state in the superconducting circuit QED system. The control scheme is based on continuous joint Zeno measurements of multiple qubits in a dispersive regime, which enables us not only to infer the state of the qubits for further information processing but also to create and stabilize the target W state through adaptive quantum feedback control. We simulate the dynamics of the proposed quantum feedback control scheme using the quantum trajectory approach with an effective stochastic maser equation obtained by a polaron-type transformation method and demonstrate that in the presence of moderate environmental decoherence, the average state fidelity higher than 0.9 can be achieved and maintained for a considerably long time (much longer than the single-qubit decoherence time). This control scheme is also shown to be robust against measurement inefficiency and individual qubit decay rate differences. Finally, the comparison of the polaron-type transformation method to the commonly used adiabatic elimination method to eliminate the cavity mode is presented.

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“…In such a general dynamical scenario the increasing attention to the existence in some bipartite systems of subradiant states that are selected pure factorized states which evolve, keeping the system in its fully initial decorrelated condition at any time instant, is not surprising. Such peculiar behavior, of both fundamental [1,2] and applicative interest [3][4][5][6][7][8], results from quantum interference effects canceling in the evolved state, at a generic time instant, exactly those contributions, stemming from the superposition principle, which, otherwise, would determine the onset and possibly the persistence of correlation manifestations between A and B. Subradiance is a cooperative effect that has been investigated both theoretically [1,2,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] and experimentally [4,[27][28][29][30][31][32] following the seminal paper by Dicke [1], mainly in radiation-matter systems, where it describes optically inactive states of an atomic ensemble (A) in an electromagnetic environment (B). The current upsurge of interest in these states reflects, indeed, the existence of many other physical contexts where this phenomenon may find promising applications [4,[33][34]…”

Section: Introductionmentioning

confidence: 99%

Interaction-free evolving states of a bipartite system

Guccione¹,

Messina

Napoli³

et al. 2014

Phys. Rev. A

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We show that two interacting physical systems may admit entangled pure or nonseparable mixed states evolving in time as if the mutual interaction Hamiltonian were absent. In this paper we define these interaction-free evolving (IFE) states and characterize their existence for a generic binary system described by a time-independent Hamiltonian. A comparison between IFE subspace and the decoherence-free subspace is reported. The set of all pure IFE states is explicitly constructed for a nonhomogeneous spin-star-system model

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Preparation of subradiant states using local qubit control in circuit QED

Cited by 47 publications

References 48 publications

Enhanced Quantum Interface with Collective Ion-Cavity Coupling

Enhanced Quantum Interface with Collective Ion-Cavity Coupling

Generation and stabilization of a three-qubit entangledWstate in circuit QED via quantum feedback control

Interaction-free evolving states of a bipartite system

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