Quantum-Dot-Based Resonant Exchange Qubit

Medford, James; Beil, J.; Taylor, Jacob M.; Rashba, Emmanuel I.; Lü, Hong; Gossard, A. C.; Marcus, C. M.

doi:10.1103/physrevlett.111.050501

Cited by 242 publications

(360 citation statements)

References 22 publications

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“…In many proposals involving single-spin qubits localized on impurity atoms [2,7] and within quantum dots [1,8], two-qubit coupling schemes harness the advantages of tunnelingbased nearest-neighbor exchange interactions: exchange gates are rapid, tunable, and protected against multiple types of noise [9][10][11][12][13]. These features have been demonstrated for electron spins in quantum dots [14][15][16][17], while a similar demonstration for spins localized on impurity atoms such as phosphorus donors in silicon remains an outstanding experimental challenge [6]. Although the exchange interaction originates from the longrange Coulomb interaction, its strength typically decays exponentially with distance [8,18].…”

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confidence: 99%

Tunable Spin-Qubit Coupling Mediated by a Multielectron Quantum Dot

Srinivasa

Taylor

2015

Phys. Rev. Lett.

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We present an approach for entangling electron spin qubits localized on spatially separated impurity atoms or quantum dots via a multi-electron, two-level quantum dot. The effective exchange interaction mediated by the dot can be understood as the simplest manifestation of RudermanKittel-Kasuya-Yosida exchange, and can be manipulated through gate voltage control of level splittings and tunneling amplitudes within the system. This provides both a high degree of tuneability and a means for realizing high-fidelity two-qubit gates between spatially separated spins, yielding an experimentally accessible method of coupling donor electron spins in silicon via a hybrid impurity-dot system.Single spins in solid-state systems represent versatile candidates for scalable quantum bits (qubits) in quantum information processing architectures [1][2][3][4][5][6]. In many proposals involving single-spin qubits localized on impurity atoms [2,7] and within quantum dots [1,8], two-qubit coupling schemes harness the advantages of tunnelingbased nearest-neighbor exchange interactions: exchange gates are rapid, tunable, and protected against multiple types of noise [9][10][11][12][13]. These features have been demonstrated for electron spins in quantum dots [14][15][16][17], while a similar demonstration for spins localized on impurity atoms such as phosphorus donors in silicon remains an outstanding experimental challenge [6]. Although the exchange interaction originates from the longrange Coulomb interaction, its strength typically decays exponentially with distance [8,18]. Long-range coupling via concatenation of multiple nearest-neighbor interactions is not ideal for coupling spatially separated electron spins, as it sets a low threshold error rate below which fault-tolerant quantum computing is feasible [19,20]. A mechanism for long-range coupling that simultaneously enables scalability and robustness against errors is therefore key to realizing practical spin-based quantum information processing devices.Approaches to implementing long-range interactions typically involve identifying a system that acts as a mediator of the interaction between the qubits, with proposed systems including optical cavities and microwave stripline resonators [21][22][23][24][25][26] [32,33], and multi-electron molecular cores [34]. Recently, long-range coupling of electrons located in the two outer quantum dots of a linear triple dot system has been demonstrated [35,36]. The effective exchange interaction in that system arises from electron cotunneling between the outer dots and exhibits the fourth-order dependence on tunneling amplitudes that is characteristic of superexchange [37], but suffers from a large virtual energy cost from the doubly occupied center dot states. In contrast, a many-electron quantum dot in the center can also couple distant spins via the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, with low-energy intermediate states [38], but perhaps at the cost of low fidelity as impurityFermi sea correlations become hard to disentangle...

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confidence: 99%

Tunable Spin-Qubit Coupling Mediated by a Multielectron Quantum Dot

Srinivasa

Taylor

2015

Phys. Rev. Lett.

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“…1 Studies of exchange-coupled electron spin qubits in GaAs QDs, in particular, have shifted their attention from the nuclear to the charge environment, as the important role of the latter has been identified. [2][3][4] Recent works include design and implementation of exchange-only three-spin qubits in a triple QD that have better immunity against low-frequency electrical noise, 5 multielectron spin qubits with demonstrated reduced exchange noise, 6 and self-calibrated, optimized pulse sequence 7 and asymmetric double dot geometry 8 , both tailored to mitigate charge noise for high-fidelity single-qubit gates in singlet-triplet (S − T 0 ) spin qubits. Charge noise was also shown to cause relaxation in a single electron spin qubit, through the spin-orbit interaction.…”

Section: Introductionmentioning

confidence: 99%

Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

Ramon

2015

Phys. Rev. B

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The effects of a collection of classical two-level charge fluctuators on the coherence of a dynamicallydecoupled qubit are studied. Distinct dynamics are found at different qubit working positions. Exact analytical formulae are derived at pure dephasing and approximate solutions are found at the general working position, for weakly-and strongly-coupled fluctuators. Analysis of these solutions, combined with numerical simulations of the multiple random telegraph processes, reveal the scaling of the noise with the number of fluctuators and the number of control pulses, as well as dependence on other parameters of the qubit-fluctuators system. These results can be used to determine potential microscopic models for the charge environment by performing noise spectroscopy.

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“…We denote this the resonant exchange (RX) qubit, and refer the reader to the concurrent Ref. [23] for an experimental demonstration of these ideas. Furthermore, our approach has a protected two-qubit interaction via exchange [24,25] or via resonant dipole-dipole interactions.…”

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confidence: 99%

Electrically Protected Resonant Exchange Qubits in Triple Quantum Dots

2013

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We present a modulated microwave approach for quantum computing with qubits comprising three spins in a triple quantum dot. This approach includes single-and two-qubit gates that are protected against low-frequency electrical noise, due to an operating point with a narrowband response to high frequency electric fields. Furthermore, existing double quantum dot advances, including robust preparation and measurement via spin-to-charge conversion, are immediately applicable to the new qubit. Finally, the electric dipole terms implicit in the high frequency coupling enable strong coupling with superconducting microwave resonators, leading to more robust two-qubit gates. PACS numbers:Spins in quantum dots as an architecture for quantum information processing require some combination of electric and magnetic field control at the nanometer scale [1]. While the intrinsic coherence properties of the spins can be remarkable, the need for such control inevitably couples the qubit degree of freedom to low-frequency electric or magnetic noise [2][3][4][5][6][7][8]. Approaches that mitigate this coupling, via dynamical decoupling or composite pulse sequences, all require rapid 'pulsed gate' control either for individual qubits or for two-qubit gates, which in turn requires wide bandwidths for the control electronics. While this has led to a variety of advances in the field, paradoxically it also leads to the use of quantum bits as sensors, rather than as protected devices [9].Instead, we suggest that the use of so-called exchangeonly qubits [10,11], comprising three spins in a triple quantum dot [12][13][14][15][16][17] and implemented experimentally [18][19][20][21], provide an opportunity for protection against low-frequency control noise in analogy to advances in superconducting devices [22]. In particular, by having exchange couplings always on, a regime with no low-frequency field response and a narrowband, resonant response becomes accessible. We denote this the resonant exchange (RX) qubit, and refer the reader to the concurrent Ref. [23] for an experimental demonstration of these ideas. Furthermore, our approach has a protected two-qubit interaction via exchange [24,25] or via resonant dipole-dipole interactions. As coupling between qubits relies on electric fields rather than tunneling, devices could be implemented in a wide variety of potential materials such as two dimensional electron gas and nanowire depletion dots. Finally, we show that the dipolar nature of the RX qubit also enables strong coupling with high quality factor microwave cavities.The few electron regime of interest for our triple dot system we describe by the Hubbard model [15](1) where U is the individual dot charging energy, U c is the cross-charging energy, V i is the local potential set by applied gate voltages on dot i, t ij is the tunneling between dots i and j, and c † iσ is the creation operator for an electron on dot i with spin σ. For simplicity, we assume a linear array and set t 12 = t l , t 23 = t r , t 13 = 0, and have defined tunneling...

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Quantum-Dot-Based Resonant Exchange Qubit

Cited by 242 publications

References 22 publications

Tunable Spin-Qubit Coupling Mediated by a Multielectron Quantum Dot

Tunable Spin-Qubit Coupling Mediated by a Multielectron Quantum Dot

Non-Gaussian signatures and collective effects in charge noise affecting a dynamically decoupled qubit

Electrically Protected Resonant Exchange Qubits in Triple Quantum Dots

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