Nonlocal Nuclear Spin Quieting in Quantum Dot Molecules: Optically Induced Extended Two-Electron Spin Coherence Time

Chow, Colin; Ross, Aaron M.; Kim, Danny; Gammon, D.; Bracker, Allan S.; Sham, L. J.; Steel, Duncan G.

doi:10.1103/physrevlett.117.077403

Cited by 23 publications

(19 citation statements)

References 39 publications

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“…1a, bottom panel). The narrow spectral feature defined by the electronic dark-state coherence thereby carves out a reduced variance Overhauser field distribution from the initial thermal state with the prospect of improved qubit coherence, as inferred from a number of experiments [6,20,21]. However, neither the direct measurement of such a distribution nor of its effect on the electron spin coherence has been achieved to date.…”

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confidence: 99%

Improving a Solid-State Qubit through an Engineered Mesoscopic Environment

et al. 2017

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A controlled quantum system can alter its environment by feedback, leading to reduced-entropy states of the environment and to improved system coherence. Here, using a quantum-dot electron spin as a control and probe, we prepare the quantum-dot nuclei under the feedback of coherent population trapping and observe their evolution from a thermal to a reduced-entropy state, with the immediate consequence of extended qubit coherence. Via Ramsey interferometry on the electron spin, we directly access the nuclear distribution following its preparation and measure the emergence and decay of correlations within the nuclear ensemble. Under optimal feedback, the inhomogeneous dephasing time of the electron, T Ã 2 , is extended by an order of magnitude to 39 ns. Our results can be readily exploited in quantum information protocols utilizing spin-photon entanglement and represent a step towards creating quantum many-body states in a mesoscopic nuclear-spin ensemble. DOI: 10.1103/PhysRevLett.119.130503 The interaction between a qubit and its mesoscopic environment offers the opportunity to access and control the ensemble properties of this environment. In turn, tailoring the environment improves qubit performance and can lead to nontrivial collective states. Significant steps towards such control have been taken in systems including nitrogenvacancy centers coupled to 13 C spins in diamond [1], superconducting qubits coupled to a microwave reservoir [2], and spins in electrostatically defined [3][4][5] and selfassembled [6] quantum dots (QDs) coupled to the host nuclei. In InGaAs QDs, the hyperfine interaction permits spin-flip processes to occur between a confined electron and the QD nuclei. Optical pumping of the electron spin induces a directional flipping of nuclear spins leading to a net polarization buildup [7]. The resulting effective magnetic (Overhauser) field can be as strong as 7 T [8], leading to significant shifts of the electron-spin energy levels [8][9][10][11]. In contrast to other systems, the polarization of this isolated mesoscopic ensemble can persist for hours [12]. Coupling the electronic energy shifts to the optical pumping rate closes a feedback loop [13][14][15][16] that allows for the selection of the degree of nuclear-spin polarization.A spectrally sharp version of such stabilizing feedback is achieved through coherent population trapping (CPT), when driving the Λ system formed by the two electronspin states and an excited trion state of a negatively charged QD [6,[17][18][19][20], as depicted in Fig. 1(a). Deviations from the dark-state resonance lead to a preferential driving of one of the two optical transitions, inducing an electron-spin polarization that pulls the Overhauser field back towards a lock point set by the two-photon resonance [ Fig. 1(a), bottom panel]. The narrow spectral feature defined by the electronic dark-state coherence thereby carves out a reduced variance Overhauser-field distribution from the initial thermal state with the prospect of improved qubit coherence, as inferr...

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confidence: 99%

Improving a Solid-State Qubit through an Engineered Mesoscopic Environment

et al. 2017

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“…Chow et al. have been able to extend the coherence for arbitrary superpositions of any of the four two‐electron ground states,

false| s false⟩, false| T_{0} false⟩, false| T_{\pm} false⟩

, in a CQD by nonlocal suppression of nuclear spin fluctuations . Using an intricate pump–probe scheme, Chow et al., were able to form a coherent state comprising all three triplet states.…”

Section: Tunable Coulomb and Exchange Interactionsmentioning

confidence: 99%

“…Within this scheme, through optical excitation localized to only one of the dots, they were able to drive the hyperfine coupling over both dots, observing ground state coherence times in excess of 1.3 µs. This nonlocal suppression of the nuclear spin fluctuations depends on the strong exchange coupling which the authors attribute as “the cause for electron‐mediated nuclear spin flip‐flop in two spatially separated QDs.”…”

Section: Tunable Coulomb and Exchange Interactionsmentioning

confidence: 99%

Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies

Jennings

Wickramasinghe

et al. 2019

Adv Quantum Tech

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Coupled quantum dots (CQDs) that consist of two InAs QDs stacked along the growth direction and separated by a relatively thin tunnel barrier have been the focus of extensive research efforts. The expansion of available states enabled by the formation of delocalized molecular wavefunctions in these systems has led to significant enhancement of the already substantial capabilities of single QD systems and have proven to be a fertile platform for studying light–matter interactions, from semi‐classical to purely quantum phenomena. Observations unique to CQDs, including tunable g‐factors and radiative lifetimes, in situ control of exchange interactions, coherent phonon effects, manipulation of multiple spins, and nondestructive spin readout, along with possibilities such as quantum‐to‐quantum transduction with error correction and multipartite entanglement, open new and exciting opportunities for CQD‐based photonic quantum technologies. This review is focused on recent CQD work, highlighting aspects where CQDs provide a unique advantage and with an emphasis on results relevant to photonic quantum technologies.

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“…There exists an extensive body of research providing evidence that the nuclear spins of InAs QDs interact with the confined electron and heavy/light hole via nonlinear feedback loops, with sensitive dependence on experimental parameters including the excitation laser frequency, polarization, power, and pulse width/repetition rate; the effects are collectively referred to as dynamic nuclear spin polarization (DNP) [6][7][8][9][10][11][12][13]. Many research groups have sought to understand, control, and reduce the impact of DNP, since it leads to loss of electron spin coherence [3][4][5][14][15][16][17][18][19]. Significantly, optically controlled fluctuation quieting has been reported [3,4,16], leading to extended electron spin coherence times up to at least 1 μs without the need for dynamical decoupling [20,21].…”

Section: Introductionmentioning

confidence: 99%