Tunable inductive coupling of superconducting qubits in the strongly nonlinear regime

Kafri, Dvir; Quintana, Chris; Chen, Yu; Shabani, Alireza; Martinis, John M.; Neven, Hartmut

doi:10.1103/physreva.95.052333

Cited by 39 publications

(33 citation statements)

References 42 publications

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“…However, their approach differs in that instead of diagnolizing the coupler Hamiltonian to solve for χ, D-Wave chooses to approximate χ as the first-order (linear) susceptibility, which can be expressed using a simple analytic formula. This approach works sufficiently well for the coupler parameters of existing D-Wave devices, but the linear approximation breaks down for larger coupler susceptibilities and coupling strengths, as discussed in reference [18].…”

Section: Mediated Couplingmentioning

confidence: 99%

“…The coupler elements [18,19,[21][22][23][24][25][26][27][28][29][30][31] are themselves also flux qubits, though operated in a regime where they can be described as a simple flux-tunable effective inductance L eff . In this language, the coupling energy between two qubits, each with persistent current I p and mutual inductance M with the coupler, is given by J = I 2 p M 2 L eff .…”

Section: Introductionmentioning

confidence: 99%

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Coherent Coupled Qubits for Quantum Annealing

et al. 2017

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Quantum annealing is an optimization technique which potentially leverages quantum tunneling to enhance computational performance. Existing quantum annealers use superconducting flux qubits with short coherence times limited primarily by the use of large persistent currents I p . Here, we examine an alternative approach using qubits with smaller I p and longer coherence times. We demonstrate tunable coupling, a basic building block for quantum annealing, between two flux qubits with small (approximately 50-nA) persistent currents. Furthermore, we characterize qubit coherence as a function of coupler setting and investigate the effect of flux noise in the coupler loop on qubit coherence. Our results provide insight into the available design space for next-generation quantum annealers with improved coherence.

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Section: Mediated Couplingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Coherent Coupled Qubits for Quantum Annealing

et al. 2017

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“…Tunable qubit-qubit coupling can be achieved in a number of ways, for example (i) by tuning two qubits directly into resonance with each other; (ii) by tuning the qubits (sequentially) into resonance with the resonator; (iii) by tuning the resonator sequentially and adiabatically into resonance with the qubits [219]; (iv) by driving the qubits with microwave radiation and coupling via sidebands; (v) by driving the qubit coupler with microwave radiation (e.g. [220]); (vi) by flux-tunable inductive (transformer) coupling [221]. In particular, for JJ-coupling, the qubit-qubit coupling can be made tunable by current-biasing the coupling JJ [218,222,223].…”

Section: Tunable Couplingmentioning

confidence: 99%

Quantum information processing with superconducting circuits: a review

2017

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During the last ten years, superconducting circuits have passed from being interesting physical devices to becoming contenders for near-future useful and scalable quantum information processing (QIP). Advanced quantum simulation experiments have been shown with up to nine qubits, while a demonstration of quantum supremacy with fifty qubits is anticipated in just a few years. Quantum supremacy means that the quantum system can no longer be simulated by the most powerful classical supercomputers. Integrated classical-quantum computing systems are already emerging that can be used for software development and experimentation, even via web interfaces. Therefore, the time is ripe for describing some of the recent development of superconducting devices, systems and applications. As such, the discussion of superconducting qubits and circuits is limited to devices that are proven useful for current or near future applications. Consequently, the centre of interest is the practical applications of QIP, such as computation and simulation in Physics and Chemistry.

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“…where ϕ q±;j = ϕ n,m +ϕ n,m+1 ±ϕ n+1,m ±ϕ n+1,m+1 . Here, inductive couplings via mutual inductances are an alternative option [54]. The full Hamiltonian of the lattice is therefore given by…”

Section: A Hamiltonian Of the Physical Latticementioning

confidence: 99%

Superconducting quantum simulator for topological order and the toric code

et al. 2017

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Topological order is now being established as a central criterion for characterizing and classifying ground states of condensed matter systems and complements categorizations based on symmetries. Fractional quantum Hall systems and quantum spin liquids are receiving substantial interest because of their intriguing quantum correlations, their exotic excitations and prospects for protecting stored quantum information against errors. Here we show that the Hamiltonian of the central model of this class of systems, the Toric Code, can be directly implemented as an analog quantum simulator in lattices of superconducting circuits. The four-body interactions, which lie at its heart, are in our concept realized via Superconducting Quantum Interference Devices (SQUIDs) that are driven by a suitably oscillating flux bias. All physical qubits and coupling SQUIDs can be individually controlled with high precision. Topologically ordered states can be prepared via an adiabatic ramp of the stabilizer interactions. Strings of qubit operators, including the stabilizers and correlations along non-contractible loops, can be read out via a capacitive coupling to read-out resonators. Moreover, the available single qubit operations allow to create and propagate elementary excitations of the Toric Code and to verify their fractional statistics. The architecture we propose allows to implement a large variety of many-body interactions and thus provides a versatile analog quantum simulator for topological order and lattice gauge theories.Topological phases of quantum matter [1,2] are of scientific interest for their intriguing quantum correlation properties, exotic excitations with fractional and non-Abelian quantum statistics, and their prospects for physically protecting quantum information against errors [3].The model which takes the central role in the discussion of topological order is the Toric Code [4-6], which is an example of a Z 2 lattice gauge theory. It consists of a two-dimensional spin lattice with quasi local fourbody interactions between the spins and features 4 g degenerate, topologically ordered ground states for a lattice on a surface of genus g. The topological order of these 4 g ground states shows up in their correlation properties. The topologically ordered states are locally indistinguishable (the reduced density matrices of a single spin are identical for all of them) and only show differences for global properties (correlations along non-contractible loops). Moreover local perturbations cannot transform these states into one another and can therefore only excite higher energy states that are separated by a finite energy gap.In equilibrium, the Toric Code ground states are therefore protected against local perturbations that are small compared to the gap, which renders them ideal candidates for storing quantum information [4]. Yet for a selfcorrecting quantum memory, the mobility of excitations needs to be suppressed as well, which so far has only been shown to be achievable in four or more lattice dimensions [7,8]...

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Tunable inductive coupling of superconducting qubits in the strongly nonlinear regime

Cited by 39 publications

References 42 publications

Coherent Coupled Qubits for Quantum Annealing

Coherent Coupled Qubits for Quantum Annealing

Quantum information processing with superconducting circuits: a review

Superconducting quantum simulator for topological order and the toric code

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