Relaxation and readout visibility of a singlet-triplet qubit in an Overhauser field gradient

Barthel, Christian; Medford, James; Bluhm, Hendrik; Yacoby, Amir; Marcus, C. M.; Hanson, M.; Gossard, A. C.

doi:10.1103/physrevb.85.035306

Cited by 53 publications

(66 citation statements)

References 33 publications

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“…DNP has been achieved experimentally by optical [84][85][86][87][88][89][90][91][92][93][94][95], electrical [83,[96][97][98][99][100], and also magnetical [101,102] driving, where it is impossible to completely list the large variety of approaches. Polarizations 50% < |p| < 70% have been reported so far [89][90][91], however, achieving |p| > 90% remains a very challenging task.…”

Section: Distribution Narrowing and Dynamic Nuclear Polarizationmentioning

confidence: 99%

“…Within the frame of this review it is sufficient to distinguish the two charge configurations (1,1) and (0,2), which denotes that the electrons are found either in different dots or both in the "right" QD, respectively. Coherent rotations |S ↔ |T 0 are induced by a magnetic field gradient between the two QDs, typically achieved by dynamic polarization of the nuclear spins [83,96,98] or by a nearby positioned micromagnet [99,100,[168][169][170]. When the barrier is reduced such that the wave functions strongly overlap, the finite exchange energy gives rise to coherent rotations |↑↓ ↔ |↓↑ , i.e., (|T 0 + |S ) / √ 2 ↔ (|T 0 − |S ) / √ 2, thus allowing for arbitrary rotations on the Bloch sphere [83].…”

Section: Two-spin Qubits (S-t0)mentioning

confidence: 99%

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Prospects for Spin-Based Quantum Computing in Quantum Dots

Kloeffel

Loss

2013

Annu. Rev. Condens. Matter Phys.

377

410

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Experimental and theoretical progress toward quantum computation with spins in quantum dots (QDs) is reviewed, with particular focus on QDs formed in GaAs heterostructures, on nanowire-based QDs, and on self-assembled QDs. We report on a remarkable evolution of the field where decoherence -one of the main challenges for realizing quantum computers -no longer seems to be the stumbling block it had originally been considered. General concepts, relevant quantities, and basic requirements for spin-based quantum computing are explained; opportunities and challenges of spin-orbit interaction and nuclear spins are reviewed. We discuss recent achievements, present current theoretical proposals, and make several suggestions for further experiments.

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Section: Distribution Narrowing and Dynamic Nuclear Polarizationmentioning

confidence: 99%

Section: Two-spin Qubits (S-t0)mentioning

confidence: 99%

Prospects for Spin-Based Quantum Computing in Quantum Dots

Kloeffel

Loss

2013

Annu. Rev. Condens. Matter Phys.

377

410

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“…In order to find a global optimum, we repeat the optimization 1000 times with randomly selected starting values. Sequences with low N seg are easier to implement experimentally, and high ∆B z are unattractive because of increased relaxation during readout [30]. Thus, low N seg and N ∆Bz can cover the relevant search space.…”

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confidence: 99%

High-Fidelity Single-Qubit Gates for Two-Electron Spin Qubits in GaAs

et al. 2014

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Single-qubit operations on singlet-triplet qubits in GaAs double quantum dots have not yet reached the fidelities required for fault-tolerant quantum information processing. Considering experimentally important constraints and using measured noise spectra, we numerically minimize the effect of decoherence (including high-frequency non-Markovian noise) and show theoretically that quantum gates with fidelities higher than 99.9% are achievable. We also present a self-consistent tuning protocol which should allow the elimination of individual systematic gate errors directly in an experiment.One well-established possibility to realize a qubit with electron spins in a semiconductor is to use the m s = 0 spin singlet and triplet states of two electrons as computational basis states [1]. In contrast to single electron spins this encoding allows for all-electrical qubit control. Very long coherence times of up to 200 µs [2], all aspects of single-qubit operation (e.g. initialization [3] and single-shot readout [4]) and a first two-qubit gate [5] have been demonstrated experimentally for such singlettriplet (ST) qubits in GaAs quantum dots. Universal single-qubit control was also shown [6] but subject to large uncharacterized errors. Limiting control error rates to ∼ 10 −3 is a crucial requirement for fault tolerant quantum computing with quantum error correction (QEC) [7][8][9]. Estimates based on coherence time measurements [2,10] indicate that very high gate fidelities should be possible for GaAs-based two-electron spin qubits. However, nonlinearities in the electric control and experimental constraints make the direct application of control methods such as Rabi driving difficult.Previous theoretical work has shown how universal control on the single-and two-qubit level can be achieved in the face of limited dynamic control range [11]. Additionally, gating sequences which are insensitive to slow (quasistatic) control fluctuations have been proposed for this qubit system [12][13][14][15]. While these proposals provide very useful conceptual guidance, a direct implementation will be impeded by experimental constraints such as finite pulse rise times and sampling rate of voltage pulses. Likewise, decoherence effects caused by charge noise [10] and nuclear spin fluctuations [16] have a significant effect.In this letter we use numerical pulse optimization to address the problems posed by systematic inaccuracies and decoherence. Pulse optimization is common in NMR [17] and is also receiving increasing attention in quantum information [12,[18][19][20][21][22][23][24]. In contrast to these previous approaches, our optimization is specifically tailored to the ST-qubit system and includes not only the relevant physical effects but also the most important hardware constraints and the effect of high-frequency nonMarkovian noise. We use experimentally determined parameters and noise spectra [10,16,25] to compute expected gate fidelities and find implementations with no systematic errors and optimized robustness to both slow and fas...

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“…The interplay between visibility, relaxation time, and pulse rise time has been investigated recently in a DQD, where DNP pulses were applied to increase the value of ∆B z due to hyperfine nuclear interaction. 25 Even though we do not specifically apply a DNP pulse sequence here prior to the qubit manipulation pulse, we know from Ref.…”

Section: Discussion Of Effects Due To Dynamical Nuclear Polarizamentioning

confidence: 99%

Visibility study ofS−T+Landau-Zener-Stückelberg oscillations without applied initialization

et al. 2015

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Probabilities deduced from quantum information studies are usually based on averaging many identical experiments separated by an initialization step. Such initialization steps become experimentally more challenging to implement as the complexity of quantum circuits increases. To better understand the consequences of imperfect initialization on the deduced probabilities, we study the effect of not initializing the system between measurements. For this we utilize Landau-ZenerStückelberg oscillations in a double quantum dot circuit. Experimental results are successfully compared to theoretical simulations.

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Relaxation and readout visibility of a singlet-triplet qubit in an Overhauser field gradient

Cited by 53 publications

References 33 publications

Prospects for Spin-Based Quantum Computing in Quantum Dots

Prospects for Spin-Based Quantum Computing in Quantum Dots

High-Fidelity Single-Qubit Gates for Two-Electron Spin Qubits in GaAs

Visibility study ofS−T+Landau-Zener-Stückelberg oscillations without applied initialization

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