Tomography of a spin qubit in a double quantum dot

Takahashi, Maki; Bartlett, Stephen D.; Doherty, Andrew C.

doi:10.1103/physreva.88.022120

Cited by 26 publications

(40 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3(a)], choosing the drive amplitude that maximizes the echo coherence time. Self-consistent two-qubit measurement and state tomography [30] (see Supplementary Information) reveal an oscillating concurrence [31] of the two-qubit state [ Fig. 3(c)].…”

mentioning

confidence: 99%

High-fidelity entangling gate for double-quantum-dot spin qubits

et al. 2017

View full text Add to dashboard Cite

Electron spins in semiconductors are promising qubits because their long coherence times enable nearly 10 9 coherent quantum gate operations. However, developing a scalable high-fidelity two-qubit gate remains challenging. Here, we demonstrate an entangling gate between two double-quantum-dot spin qubits in GaAs by using a magnetic field gradient between the two dots in each qubit to suppress decoherence due to charge noise. When the magnetic gradient dominates the voltage-controlled exchange interaction between electrons, qubit coherence times increase by an order of magnitude. Using randomized benchmarking, we measure single-qubit gate fidelities of~99%, and through self-consistent quantum measurement, state, and process tomography, we measure an entangling gate fidelity of 90%. In the future, operating double quantum dot spin qubits with large gradients in nuclear-spin-free materials, such as Si, should enable a two-qubit gate fidelity surpassing the threshold for fault-tolerant quantum information processing.npj Quantum Information (2017) 3:3 ; doi:10.1038/s41534-016-0003-1 INTRODUCTIONThe quantum phase coherence of isolated spins in semiconductors 1-7 can persist for long times, reaching tens of milliseconds for electron spins 8 and tens of minutes for nuclear spins. 9 Such long coherence times enable single-qubit gate fidelities exceeding the threshold for fault-tolerant quantum computing 8 and make spins promising qubits. However, entangling spins is difficult because magnetic interactions between spins are weak. For electrons, this challenge can be met by exploiting the charge of the electron for electric-dipole 10 or gate-controlled exchange coupling 2 between spins. In these methods, however, the qubit energy depends on electric fields, and charge noise in the host material limits singlequbit coherence.11 Charge noise also affects other qubit platforms. For example, heating due to charge noise is a limiting factor in the coherence of trapped ion qubits, 12 and the transmon superconducting qubit was designed to suppress noise from charge fluctuations in superconducting islands.13 Strategies such as composite pulses, 14, 15 dynamical decoupling, 11 and sweet-spot operation [16][17][18] have been developed to mitigate the effects of charge noise.In this work, we present a technique to suppress decoherence caused by charge noise. The key idea is to apply a large transverse qubit energy splitting that does not depend on electric fields and, therefore, suppresses the effects of charge fluctuations. We implement this scheme with two singlet-triplet qubits, each of which consists of two electrons in a double-quantum-dot.

show abstract

mentioning

confidence: 99%

High-fidelity entangling gate for double-quantum-dot spin qubits

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Usually the process of reconstructing an unknown quantum state by measurement is called quantum state tomography (QST) [1]. In the last several decades, different QST schemes have been presented including standard QST [2,3], QST by means of a single apparatus [4][5][6][7], QST on symmetric informationally complete positive-operator valued measure [8][9][10][11][12], QST on mutually unbiased bases [13][14][15], QST via unambiguous state discrimination [16], direct QST via weak measurement [17,18], QST via compressed sensing [19,20], and self-calibrating tomography [21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Determining ann-qubit state by a single apparatus through a pairwise interaction

Wang

Zheng

et al. 2014

Phys. Rev. A

View full text Add to dashboard Cite

This paper shows how one can reconstruct an unknown n-qubit state by only a single apparatus. Its core is a redistribution of the information within an extended Hilbert space by coupling the unknown system with an assistant system through only a pairwise interaction, which results in a one-to-one mapping between the unknown density matrix elements and the probabilities of the occurrence of the eigenvalues of a single, factorized observable of the composite system. In such an interaction configuration, which is more feasible in experiments, the quality of the measurement only depends on that of the subsystem consisting a of one-qubit system coupled to a one-qubit assistant. We analyze in detail the performance of this procedure and experimentally implement it for reconstructing an unknown two-qubit state using a four-nuclear-spin system.

show abstract

“…The effect of systematic measurement errors, for example [39], can comprise the security of quantum key distribution protocols [40]. Schemes which guard against measurement errors go by the name self-consistent tomography [41][42][43][44][45][46]. A recently investigated alternative is the application of classical approaches to model selection, which have been used in a variety of experimental [51,52] and theoretical [47][48][49][50] works.…”

mentioning

confidence: 99%

Quantum model averaging

Ferrie

2014

New J. Phys.

View full text Add to dashboard Cite

Standard tomographic analyses ignore model uncertainty. It is assumed that a given model generated the data and the task is to estimate the quantum state, or a subset of parameters within that model. Here we apply a model averaging technique to mitigate the risk of overconfident estimates of model parameters in two examples: (1) selecting the rank of the state in tomography and (2) selecting the model for the fidelity decay curve in randomized benchmarking.Parameter estimation is an integral part of physics. Accurate estimates of physical parameters in quantum mechanical models allow for precision quantum control [1,2] which enables practical goals such as quantum computation [3] and quantum metrology [4] which in turn can provide probes of fundamental physics such as gravity wave detection [5].Quantum parameter estimation shares many similarities with its classical counterpart. But there are many subtle and peculiar differences. Even in single parameter estimation, quantum metrology [4,7] shows that we can obtain advantages from quantum resources such as squeezed states of light [9] and entanglement [10]. With such rich structure, many new subtleties [11], considerations [12-14] and generalities [15][16][17] can arise, including entirely new approaches to estimation [18][19][20][21] and verification [22][23][24].

show abstract

Tomography of a spin qubit in a double quantum dot

Cited by 26 publications

References 31 publications

High-fidelity entangling gate for double-quantum-dot spin qubits

High-fidelity entangling gate for double-quantum-dot spin qubits

Determining ann-qubit state by a single apparatus through a pairwise interaction

Quantum model averaging

Contact Info

Product

Resources

About