Quantum Zeno effect

Itano, Wayne M.; Heinzen, D. J.; Bollinger, John J.; Wineland, David J.

doi:10.1103/physreva.41.2295

Cited by 1,134 publications

(1,055 citation statements)

References 33 publications

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“…Next, we see that the Rabi rates required for highest fidelity increase withn. This effect arises from a quantum Zeno-like competition 41 between the parity measurement which pins the qubits in the odd or even parity subspaces and the Rabi drives that try to induce transitions between these subspaces. The ratio of the rates of these processes is the quantum Zeno parameter, which must not be too large in order to ensure that the photon number selective Rabi drives correct the system fast enough.…”

Section: Simulation Of the Stabilization Protocolmentioning

confidence: 99%

Autonomously stabilized entanglement between two superconducting quantum bits

Shankar¹,

Hatridge²,

Leghtas³

et al. 2013

Nature

338

344

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Quantum error-correction codes would protect an arbitrary state of a multi-qubit register against decoherence-induced errors 1 , but their implementation is an outstanding challenge for the development of large-scale quantum computers. A first step is to stabilize a nonequilibrium state of a simple quantum system such as a qubit or a cavity mode in the presence of decoherence. Several groups have recently accomplished this goal using measurementbased feedback schemes [2][3][4][5] . A next step is to prepare and stabilize a state of a composite system [6][7][8] . Here we demonstrate the stabilization of an entangled Bell state of a quantum register of two superconducting qubits for an arbitrary time. Our result is achieved by an autonomous feedback scheme which combines continuous drives along with a specifically engineered coupling between the two-qubit register and a dissipative reservoir. Similar autonomous feedback techniques have recently been used for qubit reset 9 and the stabilization of a single qubit state 10 , as well as for creating 11 and stabilizing 6 states of multipartite quantum systems. Unlike conventional, measurement-based schemes, an autonomous approach counter-intuitively uses engineered dissipation to fight decoherence [12][13][14][15] , obviating the need 1 arXiv:1307.4349v3 [quant-ph] 23 Oct 2013 for a complicated external feedback loop to correct errors, simplifying implementation. Instead the feedback loop is built into the Hamiltonian such that the steady state of the system in the presence of drives and dissipation is a Bell state, an essential building-block state for quantum information processing. Such autonomous schemes, broadly applicable to a variety of physical systems as demonstrated by a concurrent publication with trapped ion qubits 16 , will be an essential tool for the implementation of quantum-error correction.Here we implement a proposal 17 , tailored to the circuit Quantum Electrodynamics (cQED) architecture 18 , for stabilizing entanglement between two superconducting transmon qubits 19 . The qubits are dispersively coupled to an open cavity which acts as the dissipative reservoir. The cavity in our implementation is furthermore engineered to preferentially decay into a 50 Ω transmission line that we can monitor on demand. We show, using two-qubit quantum state tomography and high-fidelity single-shot readout, that the steady-state of the system reaches the target Bell state with a fidelity of 67 %, well above the 50 % threshold that witnesses entanglement. As discussed in Ref. 17, the fidelity can be further improved by monitoring the cavity output and performing conditional tomography when the output indicates that the two qubits are in the Bell state. We implemented this protocol via post-selection and demonstrated that the fidelity increased to ∼ 77 %.Our cQED setup, outlined schematically in Fig. 1a, consists of two individually addressable qubits, Alice and Bob, coupled dispersively to a three-dimensional (3D) rectangular copper cavity.The setup is described by...

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Section: Simulation Of the Stabilization Protocolmentioning

confidence: 99%

Autonomously stabilized entanglement between two superconducting quantum bits

Shankar¹,

Hatridge²,

Leghtas³

et al. 2013

Nature

338

344

View full text Add to dashboard Cite

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“…Both the Zeno and inverse Zeno phenomena have been experimentally observed during the last few years [9,10,11,12] (but see [13] for previous analyses of experimental data on nuclear hadronic cascades). The first experiment was done with an oscillating system [9], according to an interesting proposal by Cook [14], and was widely debated [15].…”

Section: Introductionmentioning

confidence: 99%

“…The first experiment was done with an oscillating system [9], according to an interesting proposal by Cook [14], and was widely debated [15]. In a recent beautiful set of experiments, performed by Raizen's group, first the initial quadratic and non-Markovian Zeno region was observed [10], then both the quantum Zeno and inverse Zeno effects were proved for bona fide unstable system (probability leakage out of an optical potential) [11].…”

Section: Introductionmentioning

confidence: 99%

Zeno dynamics and constraints

Facchi

Marmo

Pascazio

et al. 2004

J. Opt. B: Quantum Semiclass. Opt.

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Abstract. We investigate some examples of quantum Zeno dynamics, when a system undergoes very frequent (projective) measurements that ascertain whether it is within a given spatial region. In agreement with previously obtained results, the evolution is found to be unitary and the generator of the Zeno dynamics is the Hamiltonian with hard-wall (Dirichlet) boundary conditions. By using a new approach to this problem, this result is found to be valid in an arbitrary N -dimensional compact domain. We then propose some preliminary ideas concerning the algebra of observables in the projected region and finally look at the case of a projection onto a lower dimensional space: in such a situation the Zeno ansatz turns out to be a procedure to impose constraints.

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“…This situation is very often encountered in physics, as for instance, the α-decay of a nucleus, the spontaneous emission of a photon by an excited atom, the photoelectric effect, and so on. But from the theoretical and experimental point of view, the effort has been mainly concentrated on quantum transitions between isolated levels [3] characterized by an oscillatory behavior between the different states. In this latter case the slowing down of the transition rate has, indeed, been found.…”

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confidence: 99%

Effect of the Measurement on the Decay Rate of a Quantum System

Elattari

Gurvitz

Statistical and Dynamical Aspects of Mesoscopic Systems

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We investigated the electron tunneling out of a quantum dot in the presence of a continuous monitoring by a detector. It is shown that the Schrödinger equation for the whole system can be reduced to new Bloch-type rate equations describing the time-development of the detector and the measured system at once. Using these equations we find that the continuous measurement of the unstable system does not affect its exponential decay, exp(−Γt), contrary to expectations based on the Quantum Zeno effect . However, the width of the energy distribution of the tunneling electron is no more Γ, but increases due to the decoherence, generated by the detector. It was suggested that an unstable quantum system slows down its decay rate under frequent or continuous observations [1]. This phenomenon, known as the quantum Zeno effect, is believed to be related to the projection postulate in the theory of quantum measurements [2]. Indeed, in the standard example of two-level systems, the probability of a quantum transition from an initially occupied unstable state is Q(∆t) = a(∆t) 2 . If we assume that ∆t is the measurement time, which consists in projecting the system onto the initial state, then after N successive measurements the probability of finding the unstable system in its initial state, at time t = N ∆t, is P (t) = [1 − a(∆t) 2 ] (t/∆t) . It follows from this result that P (t) → 1 for ∆t → 0, i.e. suppression of quantum transition. PACSOriginally quantum Zeno effect has been considered as a slowing down of the decay rate [1] of quantum systems in which a discrete initial state is coupled to a continuum of final states. This coupling leads to an irreversible exponential decay from the discrete state to the continuum of states. This situation is very often encountered in physics, as for instance, the α-decay of a nucleus, the spontaneous emission of a photon by an excited atom, the photoelectric effect, and so on. But from the theoretical and experimental point of view, the effort has been mainly concentrated on quantum transitions between isolated levels [3] characterized by an oscillatory behavior between the different states. In this latter case the slowing down of the transition rate has, indeed, been found. However, this was attributed to the decoherence generated by the detector without an explicit involvement of the projection postulate [4,5]. On the other hand, the slowing down of the exponential decay rate still remains a controversial issue, despite the fact that it is extensively studied [6][7][8][9] and further investigations are clearly desirable.In this letter we focus our attention on the quantum Zeno effect in exponentially decaying systems, using a microscopic description which includes the measurement devices. The latter is an essential point missed in many studies. This work is motivated by the distinct difference between continuum energy levels and discrete levels, stated above, as well as by the theoretical and experimental importance of the subject. We also propose an experimental set up which is with...

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Quantum Zeno effect

Cited by 1,134 publications

References 33 publications

Autonomously stabilized entanglement between two superconducting quantum bits

Autonomously stabilized entanglement between two superconducting quantum bits

Zeno dynamics and constraints

Effect of the Measurement on the Decay Rate of a Quantum System

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