Role of metastable charge states in a quantum-dot spin-qubit readout

Mason, J.D.; Studenikin, Sergei; Kam, A.; Wasilewski, Z. R.; Sachrajda, Andrew; Kycia, J. B.

doi:10.1103/physrevb.92.125434

Cited by 14 publications

(22 citation statements)

References 25 publications

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“…Second, it has not been demonstrated whether the signal lifetime could also be enhanced via this charge mapping process. It was reported that the expected signal enhancement was not observed in one case [20], raising doubts as to whether this process can be achieved with high fidelity. Third, the mechanisms that limit the lifetimes of the metastable states are still not understood, and a comprehensive comparison of various alternative mapping schemes is lacking.…”

Section: Introductionmentioning

confidence: 95%

“…The two-electron QD-D system can be thought of as a singlet-triplet (ST) qubit [22][23][24] in an effective double QD configuration [25] where only one of the QDs is connected directly to a charge reservoir [21]. This configuration produces latching (or hysteresis [26]) of the QD-D charge state that can be harnessed to enhance the charge detection [18][19][20] in two ways.…”

Section: Introductionmentioning

confidence: 99%

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High-Fidelity Single-Shot Readout for a Spin Qubit via an Enhanced Latching Mechanism

et al. 2018

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The readout of semiconductor spin qubits based on spin blockade is fast but suffers from a small charge signal. Previous work suggested large benefits from additional charge mapping processes; however, uncertainties remain about the underlying mechanisms and achievable fidelity. In this work, we study the single-shot fidelity and limiting mechanisms for two variations of an enhanced latching readout. We achieve average single-shot readout fidelities greater than 99.3% and 99.86% for the conventional and enhanced readout, respectively, the latter being the highest to date for spin blockade. The signal amplitude is enhanced to a full one-electron signal while preserving the readout speed. Furthermore, layout constraints are relaxed because the charge sensor signal is no longer dependent on being aligned with the conventional (2,0)-(1,1) charge dipole. Silicon donor-quantum-dot qubits are used for this study, for which the dipole insensitivity substantially relaxes donor placement requirements. One of the readout variations also benefits from a parametric lifetime enhancement by replacing the spin-relaxation process with a charge-metastable one. This provides opportunities to further increase the fidelity. The relaxation mechanisms in the different regimes are investigated. This work demonstrates a readout that is fast, has a one-electron signal, and results in higher fidelity. It further predicts that going beyond 99.9% fidelity in a few microseconds of measurement time is within reach.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

High-Fidelity Single-Shot Readout for a Spin Qubit via an Enhanced Latching Mechanism

et al. 2018

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“…Spin qubits, due to their long coherence time, have attracted much interest in the past few years. One key requirement of spin qubits is to establish a spin-to-charge conversion mechanism by which spin states can be read out using a charge sensor [24][25][26][27][28][29]. The most widely used means is spin blockade [27,28], which maps triplet and singlet states to different charge distributions across the double quantum dot (DQD).…”

Section: Introductionmentioning

confidence: 99%

“…The most widely used means is spin blockade [27,28], which maps triplet and singlet states to different charge distributions across the double quantum dot (DQD). Recently an alternative mechanism has been reported [25,26], which maps the triplet state to a metastable charge state with one electron more or less than the singlet state.…”

Section: Introductionmentioning

confidence: 99%

Enhanced readout of spin states in double quantum dot

et al. 2017

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“…Instead, we utilize an energy selective readout technique relying on relaxation of the metastable triplet state in the (1,1) configuration when pulsed into the (2,0) region. The method has been previously demonstrated in a time-averaged fashion [24][25][26]; however, we employ threshold discrimination analysis (cf., singlespin readout [27]) for single-shot readout with fidelity greater than 98%-close to fault tolerant thresholds for surface-code quantum computation [28].The device shown in Fig. 1 was fabricated using scanning tunneling microscope hydrogen lithography.…”

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confidence: 99%

High-Fidelity Single-Shot Singlet-Triplet Readout of Precision-Placed Donors in Silicon

et al. 2017

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In this work we perform direct single-shot readout of the singlet-triplet states in exchange coupled electrons confined to precision-placed donor atoms in silicon. Our method takes advantage of the large energy splitting given by the Pauli-spin blockaded (2,0) triplet states, from which we can achieve a singleshot readout fidelity of 98.4 AE 0.2%. We measure the triplet-minus relaxation time to be of the order 3 s at 2.5 T and observe its predicted decrease as a function of magnetic field, reaching 0.5 s at 1 T. DOI: 10.1103/PhysRevLett.119.046802 An increased ability to control and manipulate quantum systems is driving the field of quantum computation forward [1][2][3][4]. The spin of a single electron in the solid state has long been utilized in this context [5][6][7][8][9][10][11], providing a superbly clean quantum system with two orthogonal quantum states that can be measured with over 99% fidelity [12]. As a natural next step, the coupling of two electrons at separate sites has been studied in gate-defined quantum dots [5,13,14], as well as in donor systems [15][16][17]. In addition to being the eigenstates for two coupled spins, the singlet-triplet (ST) states of two electrons can form a qubit subspace, and have previously been utilized for quantum information processing [6,[18][19][20][21][22]. Unlike in gate-defined quantum dots, donor systems do not require electrodes to confine electrons. The resulting decrease in physical complexity makes donor nanodevices very appealing for scaling up to many electron sites [15].In the (1,1) charge configuration the ST states are eigenstates if the exchange coupling is greater than any difference in Zeeman energy between the two spins. The singlet and three triplet states are split only by the Zeeman energy in the cases of jT þ i ¼ j↑↑i and jT − i ¼ j↓↓i, and an exchange energy, J, for the singlet jSi ¼ ðj↑↓i − j↓↑iÞ= ffiffi ffi 2 p and jT 0 i ¼ ðj↑↓i þ j↓↑iÞ= ffiffi ffi 2 p states. However, in the (2,0) configuration all triplet states split from the singlet jSð2; 0Þi by a larger exchange interaction, Δ ST , measured in previous works to be > 5 meV for donors [23]. The triplet states are therefore blocked from tunneling from the ð1; 1Þ → ð2; 0Þ charge configuration, known as Pauli spin blockade.Typically, direct ST readout is performed by charge discrimination between the (1,1) and (2,0) states below the ST energy splitting Δ ST . However, this relies on the charge sensor having a large enough differential capacitive coupling to each dot to discriminate between the two charge states. This is not possible in some architectures due to symmetry constraints, in particular, for donors it is advantageous for multiple donor sites to be coupled equally to a charge sensor for independent readout and/or loading. The tightly confined electron wave function at each donor site therefore necessitates that they are equidistant from the charge sensor. As a consequence ð1; 1Þ ↔ ð2; 0Þ charge transfer signals are often too small to detect directly in this architecture.Until now s...

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Role of metastable charge states in a quantum-dot spin-qubit readout

Cited by 14 publications

References 25 publications

High-Fidelity Single-Shot Readout for a Spin Qubit via an Enhanced Latching Mechanism

High-Fidelity Single-Shot Readout for a Spin Qubit via an Enhanced Latching Mechanism

Enhanced readout of spin states in double quantum dot

High-Fidelity Single-Shot Singlet-Triplet Readout of Precision-Placed Donors in Silicon

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