Controllable freezing of the nuclear spin bath in a single-atom spin qubit

Mądzik, Mateusz T.; Ladd, Thaddeus D.; Hudson, Fay E.; Itoh, Kohei M.; Jakob, Alexander; Johnson, Brett C.; McCallum, Jeffrey C.; Jamieson, David N.; Dzurak, A. S.; Laucht, Arne; Morello, Andrea

doi:10.1126/sciadv.aba3442

Cited by 31 publications

(23 citation statements)

References 55 publications

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“…Future work will focus on integrating this method within multi-qubit systems [5,54]. We expect it will improve the fidelity in preparing highly entangled quantum states, and enable sufficient state preparation fidelity to implement quantum error correction codes [1,2] at a fault-tolerant level.…”

Section: Discussionmentioning

confidence: 99%

Beating the thermal limit of qubit initialization with a Bayesian Maxwell's demon

Johnson¹,

Mądzik²,

Hudson³

et al. 2021

Preprint

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Fault-tolerant quantum computing requires initializing the quantum register in a well-defined fiducial state. In solid-state systems, this is typically achieved through thermalization to a cold reservoir, such that the initialization fidelity is fundamentally limited by temperature. Here we present a method of preparing a fiducial quantum state that beats the thermal limit. It is based on real-time monitoring of the qubit through a negative-result measurement -the equivalent of a 'Maxwell's demon' that only triggers the experiment upon the appearance of a very cold qubit. We experimentally apply it to initialize an electron spin qubit in silicon, achieving a ground-state initialization fidelity of 98.9(4)%, a ≈ 19% improvement over the intrinsic fidelity of the system. A fidelity approaching 99.9% could be achieved with realistic improvements in the bandwidth of the amplifier chain or by slowing down the rate of electron tunneling from the reservoir. We use a nuclear spin ancilla, measured in quantum nondemolition mode, to prove the value of the electron initialization fidelity far beyond the intrinsic fidelity of the electron readout. However, the method itself does not require an ancilla for its execution, saving the need for additional resources. The quantitative analysis of the initialization fidelity reveals that a simple picture of spin-dependent electron tunneling does not correctly describe the data. Our digital 'Maxwell's demon' can be applied to a wide range of quantum systems, with minimal demands on control and detection hardware.

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Section: Discussionmentioning

confidence: 99%

Beating the thermal limit of qubit initialization with a Bayesian Maxwell's demon

Johnson¹,

Mądzik²,

Hudson³

et al. 2021

Preprint

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“…[10] Earlier studies showed that similarly low values of trap densities are retained after ion implantation, followed by a hightemperature rapid thermal anneal and a forming gas anneal. [47] The high quality of postimplantation oxides is further corroborated by the robust charge and spin properties of qubit devices based on ionimplanted donors as studied in the past decade [10][11][12][13][14][15][16]26,48]…”

Section: Single-ion Implant Detectorsmentioning

confidence: 99%

“…[12] Singlequbit error rates are in the 0.01-0.03% range, [13,14] thus addressing requirement (ii) at the 1qubit level. Conditional twoqubit operations between exchangecoupled donors elec trons have been recently demonstrated, [15] as well as universal twoqubit logic gates for donor nuclear spins with sub1% error rates. [16] In this work, we demonstrate that the industrystandard ion implantation method can be extended to the deterministic implantation of individual dopant atoms with such high confi dence to address requirement (iii) for the fabrication of donor qubit arrays with a low density of faulty or absent qubits.…”

Section: Introductionmentioning

confidence: 99%

“…[17,18] The number of addressable donor qubits has been observed to reflect the implantation fluence. [15] This follows the wellestablished prec edent of using ion implantation to introduce a wellcalibrated density of dopants in classical silicon CMOS devices. [19] We make use of the fact that ionimplanted 31 Patoms in silicon at sparse concentrations can be converted to electricallyactive sub stitutional donors with ≈100% yield [20][21][22] and sub2 nm diffu sion.…”

Section: Introductionmentioning

confidence: 99%

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Deterministic Shallow Dopant Implantation in Silicon with Detection Confidence Upper‐Bound to 99.85% by Ion–Solid Interactions

et al. 2021

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to new applications arising from the control of single charges and spins on individual dopants in silicon. Promi sing applications are where the donors function as quantum bits (qubits). How ever, configuring materials with arrays of single donor qubits in the solid state is a formidable challenge. It has been proposed that noisy, intermediatescale quantum (NISQ) [1] devices with ≈50-100 qubits can surpass classical supercom puters in executing some specific algo rithms. [2] Even for NISQ devices, the error budgets for the physical qubits are strict, requiring errors well below 1% in order to achieve sufficient circuit depths. Beyond NISQ, errorcorrected, universal quantum processors of the kind necessary to run Shor's factoring algorithm on a 2000 bit classical key will require upwards of 4000 logical qubits. Using a 2D surface code architecture, this would translate to about 200 mil lion physical qubits with present error rates of around 0.1%. [3] Future devices with lower error rates [4] will reduce the required number of physical qubits. The surface code is also able to tolerate 5-10% physically nonfunctional (absent or faulty) qubits in the architecture. [5,6] Silicon chips containing arrays of single dopant atoms can be the material of choice for classical and quantum devices that exploit single donor spins. For example, group-V donors implanted in isotopically purified 28 Si crystals are attractive for large-scale quantum computers. Useful attributes include long nuclear and electron spin lifetimes of 31 P, hyperfine clock transitions in 209 Bi or electrically controllable 123 Sb nuclear spins. Promising architectures require the ability to fabricate arrays of individual near-surface dopant atoms with high yield. Here, an on-chip detector electrode system with 70 eV root-mean-square noise (≈20 electrons) is employed to demonstrate near-room-temperature implantation of single 14 keV 31 P + ions. The physics model for the ion-solid interaction shows an unprecedented upper-bound single-ion-detection confidence of 99.85 ± 0.02% for near-surface implants. As a result, the practical controlled silicon doping yield is limited by materials engineering factors including surface gate oxides in which detected ions may stop. For a device with 6 nm gate oxide and 14 keV 31 P + implants, a yield limit of 98.1% is demonstrated. Thinner gate oxides allow this limit to converge to the upper-bound. Deterministic single-ion implantation can therefore be a viable materials engineering strategy for scalable dopant architectures in silicon devices.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202103235.

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“…Furthermore, in order to compose multi-qubit unitaries from this universal set, one must know how to do these one-and two-qubit gates without disturbing the other qubits. This is not a trivial task when the interaction between qubits cannot easily be turned off, as is the case for silicon spin qubits in some dot [16][17][18][19] and donor [20,21] systems.…”

Section: Introductionmentioning

confidence: 99%

Single-tone pulse sequences and robust two-tone shaped pulses for three silicon spin qubits with always-on exchange

Kanaar,

Wolin,

Güngördü

et al. 2021

Preprint

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Quantum computation requires high-fidelity single-qubit and two-qubit gates on a scalable platform. Silicon spin qubits are a promising platform toward realization of this goal. In this paper we show how to perform single-qubit and CZ gates in a linear chain of three spin qubits with always-on exchange coupling, which is relevant for certain dot-and donor-based silicon devices. We also show how to make the CZ gate robust against both charge noise and pulse length error using a two-tone pulse shaping method. The robust pulse maintains a fidelity of 99.99% at 3.5% fluctuations in exchange or pulse amplitude, which is an improvement over the uncorrected pulses where this fidelity can only be maintained for fluctuations in exchange up to 2% or up to 0.2% in amplitude.

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Controllable freezing of the nuclear spin bath in a single-atom spin qubit

Abstract: The quantum coherence and gate fidelity of electron spin qubits in semiconductors are often limited by nuclear spin fluctuations. Enrichment of spin-zero isotopes in silicon markedly improves the dephasing time T2* Show more

Cited by 31 publications

References 55 publications

Beating the thermal limit of qubit initialization with a Bayesian Maxwell's demon

Beating the thermal limit of qubit initialization with a Bayesian Maxwell's demon

Deterministic Shallow Dopant Implantation in Silicon with Detection Confidence Upper‐Bound to 99.85% by Ion–Solid Interactions

Single-tone pulse sequences and robust two-tone shaped pulses for three silicon spin qubits with always-on exchange

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