Fast Quantum Nondemolition Readout by Parametric Modulation of Longitudinal Qubit-Oscillator Interaction

Didier, Nicolas; Bourassa, Jérôme; Blais, Alexandre

doi:10.1103/physrevlett.115.203601

Cited by 173 publications

(257 citation statements)

References 42 publications

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“…Note that this scheme implements longitudinal coupling, an important feature for squeezing-enhanced readout 22 . Importantly, the relative sideband phase δ sets the coupling axis σ δ ≡ σ x cos δ + σ y sin δ.…”

Section: Figmentioning

confidence: 99%

Quantum dynamics of simultaneously measured non-commuting observables

Hacohen-Gourgy

Martin

Flurin

et al. 2016

Nature

152

181

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In quantum mechanics, measurements cause wavefunction collapse that yields precise outcomes, whereas for non-commuting observables such as position and momentum Heisenbergs uncertainty principle limits the intrinsic precision of a state.Although theoretical work 1 has demonstrated that it should be possible to perform simultaneous non-commuting measurements and has revealed the limits on measurement outcomes, only recently 2,3 has the dynamics of the quantum state been discussed. To realize this unexplored regime, we simultaneously apply two continuous quantum non-demolition probes of non-commuting observables to a superconducting qubit. We implement multiple readout channels by coupling the qubit to multiple modes of a cavity. To control the measurement observables, we implement a single quadrature measurement by driving the qubit and applying cavity sidebands with a relative phase that sets the observable. Here, we use this approach to show that the uncertainty principle governs the dynamics of the wavefunction by enforcing a lower bound on the measurement-induced disturbance. Consequently, as we transition from measuring identical to measuring non-commuting observables, the dynamics make a smooth transition from standard wavefunction collapse to localized persistent diffusion and then to isotropic persistent diffusion. Although the evolution of the state differs markedly from that of a conventional measurement, information about both non-commuting observables is extracted by keeping track of the time ordering of the measurement record, enabling quantum state tomography without alternating measurements. Our work creates novel capabilities for quantum control, including rapid state purification 4 , adaptive measurement 5,6 , measurement-based state steering and continuous quantum error correction 7 . As physical systems often interact continuously with their environment via non-commuting degrees of freedom, our work offers a way 8,9 to * shayhh@berkeley.edushayhh@berkeley.edu study how notions of contemporary quantum foundations 10-14 arise in such settings.In this work, we implement two high quantum efficiency readouts of the angular momenta about two different axes of an artificial spin-1/2 system and observe in real-time the resulting dynamics. Importantly, our measurements are designed to be individually quantum non-demolition, which ensures that the back-action arises only from the competition between incompatible observables.Our experiment utilizes a single superconducting transmon qubit coupled dispersively to a multimode waveguide cavity 15 . This results in a qubit-state dependent shift of the cavity mode frequency. By applying a microwave tone to a single cavity mode, one can infer the qubit state from the phase of the reflected signal 16 ; this readout scheme has been used extensively with superconducting qubits for quantum information processing, and also to perform weak measurements 17 and track quantum trajectories of a single qubit 18 . In our configuration, each cavity mode constitutes a measure...

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Section: Figmentioning

confidence: 99%

Quantum dynamics of simultaneously measured non-commuting observables

Hacohen-Gourgy

Martin

Flurin

et al. 2016

Nature

152

181

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“…Purcell decay is therefore absent [10,11] and qubit readout is truly QND [13]. The absence of qubit dressing also allows for scaling up to a lattice of arbitrary size with strictly local interactions [11].…”

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confidence: 99%

“…3(c), using single-mode squeezing at ω r and a filter at the modulation frequency, we recover the same exponential improvement found with two-mode squeezing, Eq. (5), in addition to a factor of two decrease in gate infidelity without squeezing.Interestingly, rotating the squeezing axis by π/2 when squeezing at the oscillator frequency helps in distinguishing the different oscillator states and has been shown to lead to an exponential increase in the signalto-noise ratio for qubit readout [13]. In practice, the difference between performing a two-qubit gate and a measurement is thus the parametric modulation frequency (off-resonant for the gate and on resonance for measurement) and the choice of squeezing axis.…”

mentioning

confidence: 99%

“…In Ref. [13], it was shown that modulating g z at the oscillator frequency ω r activates this interaction leading to a large qubit statedependent oscillator displacement and to fast QND qubit readout. In this paper, we show how the same approach can be used, together with single qubit rotations, for universal quantum computing by introducing a fast and high-fidelity controlled-phase gate based on longitudinal coupling.…”

mentioning

confidence: 99%

“…[13], we consider two qubits coupled to a single harmonic mode via theirσ z degree of freedom. Allowing for a time-dependent coupling, the Hamiltonian reads ( (1)…”

mentioning

confidence: 99%

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Fast and high-fidelity entangling gate through parametrically modulated longitudinal coupling

Royer

Grimsmo

Didier

et al. 2017

Quantum

Self Cite

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We investigate an approach to universal quantum computation based on the modulation of longitudinal qubit-oscillator coupling. We show how to realize a controlled-phase gate by simultaneously modulating the longitudinal coupling of two qubits to a common oscillator mode. In contrast to the more familiar transversal qubitoscillator coupling, the magnitude of the effective qubit-qubit interaction does not rely on a small perturbative parameter. As a result, this effective interaction strength can be made large, leading to short gate times and high gate fidelities. We moreover show how the gate infidelity can be exponentially suppressed with squeezing and how the entangling gate can be generalized to qubits coupled to separate oscillators. Our proposal can be realized in multiple physical platforms for quantum computing, including superconducting and spin qubits.Introduction-A widespread strategy for quantum information processing is to couple the dipole moment of multiple qubits to common oscillator modes, the latter being used to measure the qubits and to mediate longrange interactions. Realizations of this idea are found in Rydberg atoms [1], superconducting qubits [2] and quantum dots [3] amongst others. With the dipole moment operator being off-diagonal in the qubit's eigenbasis, this type of transversal qubit-oscillator coupling leads to hybridization of the qubit and oscillator degrees of freedom. In turn, this results in qubit Purcell decay [4] and to qubit readout that is not truly quantum non-demolition (QND) [5]. To minimize these problems, the qubit can be operated at a frequency detuning from the oscillator that is large with respect to the transverse coupling strength g x . This interaction then only acts perturbatively, taking a dispersive character [1]. While it has advantages, this perturbative character also results in slow oscillator-mediated qubit entangling gates [6][7][8].Rather than relying on the standard transversal coupling,Since H z commutes with the qubit's bare Hamiltonian the qubit is not dressed by the oscillator. Purcell decay is therefore absent [10,11] and qubit readout is truly QND [13]. The absence of qubit dressing also allows for scaling up to a lattice of arbitrary size with strictly local interactions [11].By itself, longitudinal interaction however only leads to a vanishingly small qubit state-dependent displacement of the oscillator field of amplitude g z /ω r 1, with ω r the oscillator frequency. In Ref.[13], it was shown that modulating g z at the oscillator frequency ω r activates this interaction leading to a large qubit statedependent oscillator displacement and to fast QND qubit readout. In this paper, we show how the same approach can be used, together with single qubit rotations, for universal quantum computing by introducing a fast and high-fidelity controlled-phase gate based on longitudinal coupling. The two-qubit logical operation relies on parametric modulation of a longitudinal qubit-oscillator coupling, inducing an effectiveσ zσz interaction between qubits co...

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Advanced Superconducting Circuits and Devices

Weides

Rotzinger

2016

Digital Encyclopedia of Applied Physics

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The article contains sections titled: Introduction Field‐Effect Devices Quantum Information Circuits Metamaterials at Microwave Frequencies Quantum Phase Slip Novel Quantum Circuits Quantum‐Limited Measurements: Microwave Parametric Amplifiers

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Fast Quantum Nondemolition Readout by Parametric Modulation of Longitudinal Qubit-Oscillator Interaction

Cited by 173 publications

References 42 publications

Quantum dynamics of simultaneously measured non-commuting observables

Quantum dynamics of simultaneously measured non-commuting observables

Fast and high-fidelity entangling gate through parametrically modulated longitudinal coupling

Advanced Superconducting Circuits and Devices

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