Realization of High-Fidelity CZ and 
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-Free iSWAP Gates with a Tunable Coupler

Sung, Youngkyu; Ding, Leon; Braumüller, Jochen; Vepsäläinen, Antti; Kannan, Bharath; Kjærgaard, Morten; Greene, Amy; Samach, Gabriel; McNally, Chris; Kim, David; Melville, Alexander; Niedzielski, Bethany; Schwartz, Maurice L.; Yoder, Jonilyn; Orlando, Terry P.; Gustavsson, Simon; Oliver, William

doi:10.1103/physrevx.11.021058

Cited by 208 publications

(127 citation statements)

References 77 publications

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“…Here we demonstrate a spin-based two qubit quantum processor with all-around high performance fidelities (readout F > 97%, simultaneous single qubit control F > 99%, and a two-qubit controlled-phase (CPHASE) gate F > 99.8%). Our two-qubit gate fidelity exceeds recent reports on spin qubits [12,13] and is competitive with superconducting qubits [14,15].…”

contrasting

confidence: 56%

“…Our demonstration represents the highest total operation fidelity in a two qubit processor realized in silicon quantum dots with performance capable of fault tolerant operation [30]. These experiments demonstrate two qubit gates with silicon spin qubits at speeds exceeding trapped ions [31] and fidelities comparable with superconducting qubits [14,15]. Given recent advances in quantum dot fabrication [16,32] spin qubits are poised to scale-up to larger multi-qubit quantum processors.…”

Section: Re(r)mentioning

confidence: 75%

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Two-qubit silicon quantum processor with operation fidelity exceeding 99%

Mills¹,

Guinn²,

Gullans³

et al. 2021

Preprint

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Silicon spin qubits satisfy the necessary criteria for quantum information processing. However, a demonstration of high fidelity state preparation and readout combined with high fidelity singleand two-qubit gates, all of which must be present for quantum error correction, has been lacking. We use a two qubit Si/SiGe quantum processor to demonstrate state preparation and readout with fidelity over 97%, combined with both single-and two-qubit control fidelities exceeding 99%. The operation of the quantum processor is quantitatively characterized using gate set tomography and randomized benchmarking. Our results highlight the potential of silicon spin qubits to become a dominant technology in the development of intermediate-scale quantum processors.

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contrasting

confidence: 56%

Section: Re(r)mentioning

confidence: 75%

Two-qubit silicon quantum processor with operation fidelity exceeding 99%

Mills¹,

Guinn²,

Gullans³

et al. 2021

Preprint

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show abstract

“…C). Meanwhile, each coupler is dynamically switched between two frequencies [58][59][60][61][62][63]: one is to turn off the effective coupling where the neighboring two qubits can be initialized and operated with single-qubit gates; the other one is to turn on the nearest-neighbor coupling to around 11 MHz for a CZ gate. After n layers of the alternating single-and two-qubit gates, we finally tune all qubits to their respective ω m j for simultaneous quantum-state measurement.…”

Section: Methodsmentioning

confidence: 99%

“…Z(θ) is realized using the virtual-Z gate, which encodes the information θ in the rotation axes of all subsequent gates [65], and is combined with CZ to assemble CR z (±π). Here, we adopt the strategy reported elsewhere [62,66] to realize the CZ gate, i.e., we diabatically tune the coupler frequency while keeping |11 and |02 (or |20 ) for the subspace of the two neighboring qubits in near resonance. The 40 ns-long CZ gate for a pair of neighboring qubits can be individually optimized to be around 0.99 in fidelity as calibrated by interleaved randomized benchmarking; when simultaneously running the CZ gates for multiple pairs of neighboring qubits as required in the experimental sequence, the averaged CZ gate fidelities can be around 0.985 as obtained by simultaneous randomized benchmarking (see Supplementary Information Tab.…”

Section: Methodsmentioning

confidence: 99%

Observation of a Floquet symmetry-protected topological phase with superconducting qubits

Deng

Zhang

Jiang

et al. 2021

Preprint

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Quantum many-body systems away from equilibrium host a rich variety of exotic phenomena that are forbidden by equilibrium thermodynamics. A prominent example is that of discrete time crystals [1-8], where time translational symmetry is spontaneously broken in periodically driven systems. Pioneering experiments have observed signatures of time crystalline phases with trapped ions [9,10], spins in nitrogen-vacancy centers [11-13], ultracold atoms [14,15], solid spin ensembles [16,17], and superconducting qubits [18-20]. Here, we report the observation of a distinct type of intrinsically non-equilibrium state of matter, a Floquet symmetry-protected topological phase, which is implemented through digital quantum simulation with an array of programmable superconducting qubits. Unlike the discrete time crystals reported in previous experiments, where spontaneous breaking of the discrete time translational symmetry occurs for local observables throughout the whole system, the Floquet symmetry-protected topological phase observed in our experiment breaks the time translational symmetry only at the boundaries and has trivial dynamics in the bulk. More concretely, we observe robust long-lived temporal correlations and sub-harmonic temporal response for the edge spins over up to 40 driving cycles using a circuit whose depth exceeds 240. We demonstrate that the sub-harmonic response is independent of whether the initial states are random product states or symmetry-protected topological states, and experimentally map out the phase boundary between the time crystalline and thermal phases. Our work paves the way to exploring novel non-equilibrium phases of matter emerging from the interplay between topology and localization as well as periodic driving, with current noisy intermediate-scale quantum processors [21].

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“…Nonetheless, in practical implementation of quantum processors, an outstanding challenge is how to maintain or even improve gate performance with growing numbers of parallel controlled qubits [1]. For quantum processors build with superconducting qubits, isolated single-qubit gates with error rates below 0.1% [2][3][4][5] and two-qubit gates with error rates approaching 0.1% [2,[6][7][8][9][10][11][12][13] have been demonstrated in various qubit architectures [2]. However, in multi-qubit systems, implementing gate operations in parallel are commonly shown worse gate performance, especially for simultaneous two-qubit gate operations applied on nearby qubits, where gate error rates are typically increased by 0.1% − 1% [14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Quantum crosstalk analysis for simultaneous gate operations on superconducting qubits

Zhao¹,

Linghu²,

Li³

et al. 2021

Preprint

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Maintaining or even improving gate performance with growing numbers of parallel controlled qubits is a vital requirement towards fault-tolerant quantum computing. For superconducting quantum processors, though isolated one-or two-qubit gates have been demonstrated with high-fidelity, implementing these gates in parallel commonly show worse performance. Generally, this degradation is attributed to various crosstalks between qubits, such as quantum crosstalk due to residual inter-qubit coupling. An understanding of the exact nature of these crosstalks is critical to figuring out respective mitigation schemes and improved qubit architecture designs with low crosstalk. Here we give a theoretical analysis of quantum crosstalk impact on simultaneous gate operations in a qubit architecture, where fixed-frequency transmon qubits are coupled via a tunable bus, and sub-100-ns controlled-Z (CZ) gates can be realized by applying a baseband flux pulse on the bus. Our analysis shows that for microwave-driven single qubit gates, the dressing from qubit-qubit coupling can cause nonnegligible cross-driving errors when qubits operate near frequency collision regions. During CZ gate operations, although unwanted near-neighbor interactions are nominally turned off, sub-MHz parasitic next-near-neighbor interactions involving spectator qubits can still exist, causing considerable leakage or control error when one operates qubit systems around these parasitic resonance points. To ensure high-fidelity simultaneous operations, this could rise a request to figure out a better way to balance the gate error from target qubit systems themselves and the error from non-participating spectator qubits. Overall, our analysis suggests that towards useful quantum processors, the qubit architecture should be examined carefully in the context of high-fidelity simultaneous gate operations in a scalable qubit lattice.

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Realization of High-Fidelity CZ and ZZ -Free iSWAP Gates with a Tunable Coupler

Cited by 208 publications

References 77 publications

Two-qubit silicon quantum processor with operation fidelity exceeding 99%

Two-qubit silicon quantum processor with operation fidelity exceeding 99%

Observation of a Floquet symmetry-protected topological phase with superconducting qubits

Quantum crosstalk analysis for simultaneous gate operations on superconducting qubits

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