Entanglement across separate silicon dies in a modular superconducting qubit device

Abstract

Assembling future large-scale quantum computers out of smaller, specialized modules promises to simplify a number of formidable science and engineering challenges. One of the primary challenges in developing a modular architecture is in engineering high fidelity, low-latency quantum interconnects between modules. Here we demonstrate a modular solid state architecture with deterministic inter-module coupling between four physically separate, interchangeable superconducting qubit integrated circuits, achieving two-qubit gate fidelities as high as 99.1 ± 0.5% and 98.3 ± 0.3% for iSWAP and CZ entangling gates, respectively. The quality of the inter-module entanglement is further confirmed by a demonstration of Bell-inequality violation for disjoint pairs of entangled qubits across the four separate silicon dies. Having proven out the fundamental building blocks, this work provides the technological foundations for a modular quantum processor: technology which will accelerate near-term experimental efforts and open up new paths to the fault-tolerant era for solid state qubit architectures.

Building Blocks of a Flip-Chip Integrated Superconducting Quantum Processor

“…Our demonstrated average gate fidelities in flip-chip are comparable to those obtained in single-chip devices [19] and those reported by other groups in flip-chip modules [1,2,9,12,38]. In particular, the short gate duration in Ref.…”

“…This indicates that the qubit coherence times are yet to be affected by the additional flip-chip fabrication step. These coherence times compare favourably to values reported for flip-chip devices by other groups [1,2,9,11,12,21,40]. Further work aiming to improve qubit coherence times within a flip-chip includes device design and process development, in particular to reduce the loss contribution of dielectrics, alternative materials, and the investigation of other device concepts such as the fluxonium [41].…”

“…Two other scalable 3D-integration approaches are multi-chip (flip-chip or interposer chip) circuits and out-of-plane wiring [1,2,[8][9][10][11][12][13][14][15][16]. Both approaches have the advantage that the chip hosting the quantum circuitry can be fabricated separately, with minimal extra processing that risks degrading qubit performance.…”

“…Multi-chip implementations [1,2,[8][9][10][11][12] typically separate the quantum and the input/output wiring circuitry onto different chips. These chips are then connected to each other in a multi-chip module by flip-chip bump-bonding techniques.…”

Gralmonium: Granular Aluminum Nano-Junction Fluxonium Qubit

“…The remarkable progress of superconducting quantum information processing in academia [1][2][3][4][5][6][7][8][9] and in companies [10][11][12][13] is fueled by the Josephson effect [14], which provides nonlinearity while maintaining coherence. In practice, the vast majority of JJs are implemented in the form of Al/AlO x /Al SIS weak links, which offer a long list of benefits, such as high control over the insulating barrier [15], robustness to thermal cycling [16] and unmatched coherence [16][17][18][19].…”