Decoherence of a qubit by non-Gaussian noise at an arbitrary working point

Bergli, Joakim; Galperin, Y. M.; Altshuler, B. L.

doi:10.1103/physrevb.74.024509

Cited by 50 publications

(54 citation statements)

References 20 publications

(21 reference statements)

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“…47, we explain these collective effects by recalling the nonlinear dependence of the Hamiltonian eigenvalues in the qubit-TLF couplings, Eq. (23).…”

Section: Two or More Fluctuatorsmentioning

confidence: 99%

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Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

Ramon

2015

Phys. Rev. B

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The effects of a collection of classical two-level charge fluctuators on the coherence of a dynamicallydecoupled qubit are studied. Distinct dynamics are found at different qubit working positions. Exact analytical formulae are derived at pure dephasing and approximate solutions are found at the general working position, for weakly-and strongly-coupled fluctuators. Analysis of these solutions, combined with numerical simulations of the multiple random telegraph processes, reveal the scaling of the noise with the number of fluctuators and the number of control pulses, as well as dependence on other parameters of the qubit-fluctuators system. These results can be used to determine potential microscopic models for the charge environment by performing noise spectroscopy.

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“…47, we explain these collective effects by recalling the nonlinear dependence of the Hamiltonian eigenvalues in the qubit-TLF couplings, Eq. (23).…”

Section: Two or More Fluctuatorsmentioning

confidence: 99%

“…47 Denoting the sum of the contributions from all TLFs as v nT (t) = nT i=1 v i ξ i (t), the eigenvalues of the Hamiltonian, Eq. (1), read…”

Section: B Many Fluctuatorsmentioning

confidence: 99%

Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

Ramon

2015

Phys. Rev. B

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“…This has been considered by several authors [6,7,8,9]. For the most part, these authors considered the case of pure dephasing noise.…”

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confidence: 99%

Noise-induced looping on the Bloch sphere: Oscillatory effects in dephasing of qubits subject to broad-spectrum noise

Zhou

Joynt

2010

Phys. Rev. A

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For many implementations of quantum computing, 1/f and other types of broad-spectrum noise are an important source of decoherence. An important step forward would be the ability to back out the characteristics of this noise from qubit measurements and to see if it leads to new physical effects. For certain types of qubits, the working point of the qubit can be varied. Using a new mathematical method that is suited to treat all working points, we present theoretical results that show how this degree of freedom can be used to extract noise parameters and to predict a new effect: noise-induced looping on the Bloch sphere. We analyze data on superconducting qubits to show that they are very near the parameter regime where this looping should be observed.PACS numbers: 85.25. Cp, 03.65.Yz, 75.10.Jm Motivated by the prospect of quantum computation and communication, coherent quantum operation and control of small systems has become a central area of physics research. The isolation of these systems from external noise is a key problem, as noise produces decoherence. In solid-state systems, some level of 1/f or other broad-spectrum noise (BSN) is almost always present, and is typically difficult to eliminate [1]. Indeed, in superconducting qubits, single-electron and other tunneling devices, this type of noise is recognized as the factor chiefly responsible for dephasing [2,3,4,5].One interesting question is the extent to which the characteristics of the BSN can be determined by measurements on the qubit itself. This has been considered by several authors [6,7,8,9]. For the most part, these authors considered the case of pure dephasing noise. Some theoretical work has been done for "mixed" noise, which causes both relaxation and dephasing, but this has usually been limited to Gaussian approximations [10], asymptotic analysis, or small numbers of RTNs [11].In this Letter, we show how to treat mixed noise analytically for all times, fully taking into account the nonGaussian effects. This will enable us to show how to back out the characteristics of the noise from qubit measurements. A new physical effect is predicted: noise-induced looping on the Bloch sphere. We shall analyze data on superconducting flux qubits to show that they are close to the regime in which this effect comes into play. However, we stress that this effect can occur in any two-level system that is subject to BSN, which can include qubit implementation from atomic and molecular physics as well as solid-state ones.The effective Hamiltonian of a qubit is often written, where ε and ∆ are the energy difference and tunneling splitting between the two physical states. For example, in a flux qubit ε is proportional to the applied flux through the superconducting loop and ∆ is the Josephson coupling. h ′ (t) is the noise, a random function. We shall be interested in the case where h ′ (t) comes from K random telegraph noise sources (RTNs) with a wide range of switching frequencies, giving rise to BSN. The coordinate system will be rotated by the angle θ = tan...

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“…In this Letter, we investigate coherence properties of such an optically illuminated nuclear spin-electron spin system. We show that these properties are well-described by a spin-fluctuator model [9,10,11,12], involving a single nuclear spin (system) coupled by the hyperfine interaction to an electron [13] (fluctuator) that undergoes rapid optical transitions and mediates the coupling between the nuclear spin and the environment. We generalize the spin-fluctuator model to a vector description, necessary for single NV centers in diamond [1], and make direct comparisons with experiments.…”

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confidence: 99%

Coherence of an Optically Illuminated Single Nuclear Spin Qubit

et al. 2008

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We investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt et al., Science, 316, 1312] when a proximal electronic spin associated with a nitrogenvacancy (NV) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment.Nuclear spins are of fundamental importance for storage and processing of quantum information. Their excellent coherence properties make them a superior qubit candidate even in room temperature solids. Unfortunately, their weak coupling to the environment also makes it difficult to isolate and manipulate individual nuclei. Recently, coherent preparation, manipulation and readout of individual 13 C nuclear spins in the diamond lattice were demonstrated [1,2]. These experiments make use of optical polarization and manipulation of the electronic spin associated with a nitrogen-vacancy (NV) color center in the diamond lattice [3,4,5,6]. This enables reliable control of the nuclear spin qubit via hyperfine interactions with the electronic spin.In order to be useful for applications in scalable quantum information processing [3], such as quantum communication [7] and quantum computation [8], the quantum coherence of the nuclear spins must be maintained even when the electronic state is undergoing fast transitions associated with optical measurement and with entanglement generation between electronic spins. In this Letter, we investigate coherence properties of such an optically illuminated nuclear spin-electron spin system. We show that these properties are well-described by a spin-fluctuator model [9,10,11,12], involving a single nuclear spin (system) coupled by the hyperfine interaction to an electron [13] (fluctuator) that undergoes rapid optical transitions and mediates the coupling between the nuclear spin and the environment. We generalize the spin-fluctuator model to a vector description, necessary for single NV centers in diamond [1], and make direct comparisons with experiments. Most importantly we demonstrate that the decoherence of the nuclear spin due to the rapidly fluctuating electron is greatly suppressed via a mechanism analogous to motional narrowing in nuclear magnetic resonance (NMR) [14,15], allowing the nuclear spin coherence to be preserved even after hundreds of optical excitation cycles. We further show that by proper tuning of experimental parameters it may be possible to completely decouple the nuclear spin system from the electronic environment. The spinfluctuator model discussed here ...

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Decoherence of a qubit by non-Gaussian noise at an arbitrary working point

Cited by 50 publications

References 20 publications

Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

Noise-induced looping on the Bloch sphere: Oscillatory effects in dephasing of qubits subject to broad-spectrum noise

Coherence of an Optically Illuminated Single Nuclear Spin Qubit

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