Quantum-bath-driven decoherence of mixed spin systems

Balian, S. J.; Wolfowicz, Gary; Morton, John J. L.; Monteiro, T. S.

doi:10.1103/physrevb.89.045403

Cited by 39 publications

(94 citation statements)

References 45 publications

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“…At CTs, the effect of the 29 Si on the electron spin coherence is strongly suppressed (though not completely removed), leading to coherence times of up to 100 ms. Previous studies have focused on quantum approaches to model electron spin decoherence from 29 Si nuclear spin baths [24,25]; however, performing such calculations near the CTs can be challenging due to the strongly correlated nuclear spin baths [24].…”

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Classical nature of nuclear spin noise near clock transitions of Bi donors in silicon

Wolfowicz

et al. 2015

Phys. Rev. B

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Whether a quantum bath can be approximated as classical Gaussian noise is a fundamental issue in central spin decoherence and also of practical importance in designing noise-resilient quantum control. Spin qubits based on bismuth donors in silicon have tunable interactions with nuclear spin baths and are first-order insensitive to magnetic noise at so-called clock transitions (CTs). This system is therefore ideal for studying the quantum/classical Gaussian nature of nuclear spin baths since the qubit-bath interaction strength determines the back-action on the baths and hence the adequacy of a Gaussian noise model. We develop a Gaussian noise model with noise correlations determined by quantum calculations and compare the classical noise approximation to the full quantum bath theory. We experimentally test our model through a dynamical decoupling sequence of up to 128 pulses, finding good agreement with simulations and measuring electron spin coherence times approaching 1 s-notably using natural silicon. Our theoretical and experimental study demonstrates that the noise from a nuclear spin bath is analogous to classical Gaussian noise if the back-action of the qubit on the bath is small compared to the internal bath dynamics, as is the case close to CTs. However, far from the CTs, the back-action of the central spin on the bath is such that the quantum model is required to accurately model spin decoherence. Introduction. Central spin decoherence due to coupling to the environment is not only a central issue in understanding quantum-to-classical transitions [1,2], but also one of the key challenges in the realization of quantum computation [3]. There are two distinct models to describe the decoherence processes in such cases: in the semiclassical model, the central spin accumulates random phases due to thermal or quantum fluctuations of the environment [4,5], while in the quantum model, the coupling between the central spin and the environment produces entanglement and results in leakage of the which-way information from the central spin to the environment [6][7][8][9]. The fundamental difference between these two models lies in the fact that the classical noise is independent of the central spin state while the quantum noise is governed by the difference of environmental Hamiltonians conditioned on the qubit state, called the back-action from the central spin [10,11].The classical noise model of quantum baths, especially the Gaussian stochastic noise model, is a useful approximation in designing noise-resilient quantum control [12], which would otherwise require a large amount of numerical simulations of many-body dynamics of quantum baths. Dynamical decoupling has been employed to extract the noise spectra of baths [13][14][15][16][17], which are in turn used to design optimal quantum control for protecting quantum coherence and quantum gates. The viability of such methods critically

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“…For the Si:Bi system interacting with a 29 Si nuclear spin bath (I i = 1/2 and natural abundance 4.7% throughout the host lattice), the system Hamiltonian is divided into three parts [24,25]:…”

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Classical nature of nuclear spin noise near clock transitions of Bi donors in silicon

Wolfowicz

et al. 2015

Phys. Rev. B

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“…The quantum dynamics of a single qubit or central spin coupled to a spin environment [1] has been widely studied theoretically in several different areas, including quantum information sciences [2][3][4][5][6][7][8][9], quantum decoherence [10][11][12][13][14][15][16][17][18][19], and excitation energy transfer [20][21][22]. One of the most promising candidates for quantum computation, solidstate spin systems, are inevitably coupled to their surrounding environment, usually through interactions with neighboring nuclear spins [6,23,24].…”

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Rabi oscillations, decoherence, and disentanglement in a qubit–spin-bath system

Nanduri

Rabitz

2014

Phys. Rev. A

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We examine the influence of environmental interactions on simple quantum systems by obtaining the exact reduced dynamics of a qubit coupled to a one-dimensional spin bath. In contrast to previous studies, both the qubit-bath coupling and the nearest neighbor intrabath couplings are taken as the spin-flip XX-type. We first study the Rabi oscillations of a single qubit with the spin bath prepared in a spin coherent state, finding that nonresonance and finite intrabath interactions have significant effects on the qubit dynamics. Next, we discuss the bath-induced decoherence of the qubit when the bath is initially in the ground state, and show that the decoherence properties depend on the internal phases of the spin bath. By considering two independent copies of the qubitbath system, we finally probe the disentanglement dynamics of two noninteracting entangled qubits. We find that entanglement sudden death appears when the spin bath is in its critical phase. We show that the single-qubit decoherence factor is an upper bound for the two-qubit concurrence.

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“…A particularly striking example has been identified recently in spin systems with special coherence sweet-spots termed 'optimal working points' (OWPs), [10][11][12][13][14] where theory and experiment found that coherence times can change by orders of magnitude with even small variations in applied magnetic field (∼ 200 G). A drastic change in back-action occurs via changes to the states of the central spin only: the change in external field has little direct effect on the bath spin-pair dynamics.…”

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“…45 It is thus also of practical importance to understand whether dynamical decoupling and OWP techniques may be advantageously combined for a quantum bath of nuclear spins. For donor electronic qubits in silicon, it is known that due to inhomogeneous broadening from naturally-occurring 29 Si spin isotopes, there is a significant gap between the T 2 ∼ 100 ms in natural silicon near an OWP, 12,13 and the T 2 ∼ 2 s in isotopically enriched 28 Si with a low donor concentration at the same OWP. 13 Also, dynamical decoupling may be useful when it is convenient to operate with the magnetic field close to but not exactly at the OWP.…”

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Keeping a spin qubit alive in natural silicon: Comparing optimal working points and dynamical decoupling

2015

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There are two distinct techniques of proven effectiveness for extending the coherence lifetime of spin qubits in environments of other spins. One is dynamical decoupling, whereby the qubit is subjected to a carefully timed sequence of control pulses; the other is tuning the qubit towards 'optimal working points' (OWPs), which are sweet-spots for reduced decoherence in magnetic fields. By means of quantum many-body calculations, we investigate the effects of dynamical decoupling pulse sequences far from and near OWPs for a central donor qubit subject to decoherence from a nuclear spin bath. Key to understanding the behavior is to analyse the degree of suppression of the usually dominant contribution from independent pairs of flip-flopping spins within the many-body quantum bath. We find that to simulate recently measured Hahn echo decays at OWPs (lowestorder dynamical decoupling), one must consider clusters of three interacting spins, since independent pairs do not even give finite T2 decay times. We show that while operating near OWPs, dynamical decoupling sequences require hundreds of pulses for a single order of magnitude enhancement of T2, in contrast to regimes far from OWPs, where only about ten pulses are required.

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Quantum-bath-driven decoherence of mixed spin systems

Cited by 39 publications

References 45 publications

Classical nature of nuclear spin noise near clock transitions of Bi donors in silicon

Classical nature of nuclear spin noise near clock transitions of Bi donors in silicon

Rabi oscillations, decoherence, and disentanglement in a qubit–spin-bath system

Keeping a spin qubit alive in natural silicon: Comparing optimal working points and dynamical decoupling

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