Realization of a 
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 System with Metastable States of a Capacitively Shunted Fluxonium

Earnest, Nathan; Chakram, Srivatsan; Lu, Yao; Irons, Nicholas J.; Naik, Ravi; Leung, Nelson; Ocola, Leonidas E.; Czaplewski, David A.; Baker, Brian; Lawrence, Jay; Koch, Jens; Schuster, David I.

doi:10.1103/physrevlett.120.150504

Cited by 118 publications

(115 citation statements)

References 42 publications

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“…Accordingly, we adopt a baseline superconducting noise model, labeled as SC, corresponding to a superconducting device which has 10x lower gate errors and 10x longer T 1 duration than the current IBM hardware. This range of parameters has already been achieved experimentally in superconducting devices for gate errors [55,56] and for T 1 duration [57,58] independently. Faster gates Noise Model 3p 1 15p 2 T 1 SC 10 −4 10 −3 1 ms SC+T1 10 −4 10 −3 10 ms SC+GATES 10 −5 10 −4 1 ms SC+T1+GATES 10 −5 10 −4 10 ms Table 2: Noise models simulated for superconducting devices.…”

Section: Superconducting Qcmentioning

confidence: 53%

Asymptotic improvements to quantum circuits via qutrits

Gokhale

Baker

Duckering

et al. 2019

Proceedings of the 46th International Symposium on Computer Architecture

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Quantum computation is traditionally expressed in terms of quantum bits, or qubits. In this work, we instead consider three-level qutrits. Past work with qutrits has demonstrated only constant factor improvements, owing to the log 2 (3) binary-to-ternary compression factor. We present a novel technique using qutrits to achieve a logarithmic depth (runtime) decomposition of the Generalized Toffoli gate using no ancilla-a significant improvement over linear depth for the best qubit-only equivalent. Our circuit construction also features a 70x improvement in two-qudit gate count over the qubit-only equivalent decomposition. This results in circuit cost reductions for important algorithms like quantum neurons and Grover search. We develop an open-source circuit simulator for qutrits, along with realistic near-term noise models which account for the cost of operating qutrits. Simulation results for these noise models indicate over 90% mean reliability (fidelity) for our circuit construction, versus under 30% for the qubit-only baseline. These results suggest that qutrits offer a promising path towards scaling quantum computation. CCS CONCEPTS• Computer systems organization → Quantum computing. KEYWORDS quantum computing, quantum information, qutrits ACM Reference Format:

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Section: Superconducting Qcmentioning

confidence: 53%

Asymptotic improvements to quantum circuits via qutrits

Gokhale

Baker

Duckering

et al. 2019

Proceedings of the 46th International Symposium on Computer Architecture

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“…The simplest manifestations involve improving quality factors associated with coupling to different thermal baths [42,48,49] and reducing noise spectral densities for different Hamiltonian parameters [13,50,51]. At a higher level, a popular approach to suppressing qubit relaxation has been to localize wavefunctions in disparate regions of phase space to lessen transition matrix elements [28,30,36,52]. On the other hand, delocalization of the same wavefunctions has been shown to mitigate dephasing effects by reducing qubit sensitivity to Hamiltonian parameters [10,18,43,[53][54][55].…”

Section: A Protectionmentioning

confidence: 99%

Superconducting circuit protected by two-Cooper-pair tunneling

Smith

Kou

et al. 2020

npj Quantum Inf

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We present a protected superconducting qubit based on an effective circuit element that only allows pairs of Cooper pairs to tunnel. These dynamics give rise to a nearly degenerate ground state manifold indexed by the parity of tunneled Cooper pairs. We show that, when the circuit element is shunted by a large capacitance, this manifold can be used as a logical qubit that we expect to be insensitive to multiple relaxation and dephasing mechanisms.

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“…In contrast to the transmon, heavy fluxonium combines strong Josephson non-linearity with T 1 protection due to disjoint support of its lowest-lying localized wave functions. Heavy fluxonium devices utilize a decreased capacitive energy E C , which emphasizes the localization of states [28,30]. Moreover, fluxonium eigenenergies are intrinsically insensitive to slow offset charge variations [47].…”

Section: A Single-qubit Gatesmentioning

confidence: 99%

“…Experimentally, gates for heavy fluxonium have been realized by driving Raman transitions [28,29], which utilize intermediary higher-energy states to assist indirect transitions between the protected states. We will demonstrate a similar approach, exploiting the availability of intermediary state transitions using optimal control theory.…”

Section: A Single-qubit Gatesmentioning

confidence: 99%

Universal gates for protected superconducting qubits using optimal control

et al. 2020

Self Cite

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We employ quantum optimal control theory to realize quantum gates for two protected superconducting circuits: the heavy-fluxonium qubit and the 0-π qubit. Utilizing automatic differentiation facilitates the simultaneous inclusion of multiple optimization targets, allowing one to obtain high-fidelity gates with realistic pulse shapes. For both qubits, disjoint support of low-lying wave functions prevents direct population transfer between the computational-basis states. Instead, optimal control favors dynamics involving higher-lying levels, effectively lifting the protection for a fraction of the gate duration. For the 0-π qubit, offset-charge dependence of matrix elements among higher levels poses an additional challenge for gate protocols. To mitigate this issue, we randomize the offset charge during the optimization process, steering the system towards pulse shapes insensitive to charge variations. Closed-system fidelities obtained are 99% or higher, and show slight reductions in open-system simulations.

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Realization of a Λ System with Metastable States of a Capacitively Shunted Fluxonium

Cited by 118 publications

References 42 publications

Asymptotic improvements to quantum circuits via qutrits

Asymptotic improvements to quantum circuits via qutrits

Superconducting circuit protected by two-Cooper-pair tunneling

Universal gates for protected superconducting qubits using optimal control

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