Tunable joint measurements in the dispersive regime of cavity QED

Lalumière, Kevin; Gambetta, Jay; Blais, Alexandre

doi:10.1103/physreva.81.040301

Cited by 74 publications

(117 citation statements)

References 31 publications

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“…While powerful, this measurement protocol is binary and instantaneous, and it allows no insight into the dynamical processes underlying the generation of the entangled state. In solid-state systems, such as superconducting qubit transitions in the microwave regime, there has been tremendous interest in continuously generating bipartite [3][4][5][6]39] and multipartite [2,40,41] entangled states, using weak measurements that slowly interact with the qubits, in such a way that enables the resolution of the dynamical aspects of the entangling backaction. Analog feedback control can naturally be applied in the weak continuousmeasurement regimes [42][43][44], and digital feedbackgenerated entanglement has already been demonstrated [45].…”

Section: Introductionmentioning

confidence: 99%

Quantum Trajectories and Their Statistics for Remotely Entangled Quantum Bits

et al. 2016

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We experimentally and theoretically investigate the quantum trajectories of jointly monitored transmon qubits embedded in spatially separated microwave cavities. Using nearly quantum-noise-limited superconducting amplifiers and an optimized setup to reduce signal loss between cavities, we can efficiently track measurement-induced entanglement generation as a continuous process for single realizations of the experiment. The quantum trajectories of transmon qubits naturally split into low and high entanglement classes. The distribution of concurrence is found at any given time, and we explore the dynamics of entanglement creation in the state space. The distribution exhibits a sharp cutoff in the high concurrence limit, defining a maximal concurrence boundary. The most-likely paths of the qubits' trajectories are also investigated, resulting in three probable paths, gradually projecting the system to two even subspaces and an odd subspace, conforming to a "half-parity" measurement. We also investigate the most-likely time for the individual trajectories to reach their most entangled state, and we find that there are two solutions for the local maximum, corresponding to the low and high entanglement routes. The theoretical predictions show excellent agreement with the experimental entangled-qubit trajectory data.

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Section: Introductionmentioning

confidence: 99%

Quantum Trajectories and Their Statistics for Remotely Entangled Quantum Bits

et al. 2016

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“…1). The system can be described well by the Tavis-Cummings model [9,38,43,45,51,52] and the Hamiltonian driven by a measurement signal is described by…”

Section: System: Hamiltonian and Stochastic Master Equationmentioning

confidence: 99%

“…Moreover, previous investigations were performed in a parameter regime of a strongly damped resonator cavity so one can adiabatically eliminate the cavity mode by enslaving the cavity to qubit dynamics [42,43,[47][48][49]. Here we go beyond this socalled bad-cavity limit by using a polaron-type transformation [38,50] to trace out the cavity mode in our analysis. This allows us to work in a parameter regime in which the W state can be maintained with higher fidelity.…”

Section: Introductionmentioning

confidence: 99%

“…Generation and manipulation of entangled states are important tasks of quantum information processing. Besides the scheme based on unitary dynamics to generate entangled states [7,34,35], there are proposals of entanglement generation by measurement [36][37][38]. Although measurements can generate entangled states that are otherwise difficult to obtain, the specific or target entangled states created are primarily probabilistic.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Of particular interest is the parity measurement [12][13][14] that discriminates between states in a multiqubit register with even or odd total excitation number. Parity measurement on four data qubits at the corners of every square tile on a lattice is needed to realize surface codes, offering the highest faulttolerance thresholds to date [15,16].…”

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confidence: 99%

Entanglement Genesis by Ancilla-Based Parity Measurement in 2D Circuit QED

et al. 2014

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We present an indirect two-qubit parity meter in planar circuit quantum electrodynamics, realized by discrete interaction with an ancilla and a subsequent projective ancilla measurement with a dedicated, dispersively coupled resonator. Quantum process tomography and successful entanglement by measurement demonstrate that the meter is intrinsically quantum nondemolition. Separate interaction and measurement steps allow the execution of subsequent data-qubit operations in parallel with ancilla measurement, offering time savings over continuous schemes. DOI: 10.1103/PhysRevLett.112.070502 PACS numbers: 03.67.Bg, 03.67.Lx, 42.50.Pq, 85.25.-j Controlling the entanglement between qubits is central to the development of every quantum computing architecture. Early efforts with superconducting quantum circuits relied on quantum interference for this purpose. Programmed sequences of one-and few-qubit gates fitting within qubit coherence times have allowed the generation of two-and three-qubit entanglement [1][2][3][4] and the implementation of elementary quantum algorithms [5][6][7][8][9] and games [10].Recently, focus has shifted toward generating and preserving entanglement by nondemolition measurement of multiqubit observables and their use in feedback loops as required for quantum error correction [11]. Of particular interest is the parity measurement [12][13][14] that discriminates between states in a multiqubit register with even or odd total excitation number. Parity measurement on four data qubits at the corners of every square tile on a lattice is needed to realize surface codes, offering the highest faulttolerance thresholds to date [15,16].A convenient approach to implementing a parity measurement is a two-step indirect scheme involving coherent interaction of the data qubits with an ancillary qubit and subsequent strong measurement of this ancilla. To date, indirect four-qubit parity measurements have been achieved only in trapped-ion systems [17]. In the solid state, parity measurement using an ancillary electron spin has been used to generate probabilistic entanglement between two nuclear spins in nitrogen-vacancy centers in diamond [18]. More recently, parity measurement of two transmon qubits using a dispersively coupled 3D cavity has been used in a digital feedback loop to generate entanglement deterministically [19]. An important next step is the realization of parity measurements in an architecture amenable to surface coding.In this Letter, we present an ancilla-based two-qubit parity measurement in a planar circuit QED (cQED) architecture [20]. Tomographic characterization shows that dephasing within even and odd parity subspaces is due to intrinsic qubit decoherence during interaction and measurement steps, making the parity meter intrinsically quantum nondemolition (QND). As a further demonstration of this nondemolition character, we generate entanglement by parity measurement on a maximal superposition state. Performing all tomographic data-qubit operations after the ancilla measurement, we achi...

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Tunable joint measurements in the dispersive regime of cavity QED

Cited by 74 publications

References 31 publications

Quantum Trajectories and Their Statistics for Remotely Entangled Quantum Bits

Quantum Trajectories and Their Statistics for Remotely Entangled Quantum Bits

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

Entanglement Genesis by Ancilla-Based Parity Measurement in 2D Circuit QED

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