Realizing all-to-all couplings among detachable quantum modules using a microwave quantum state router

Abstract

One of the primary challenges in realizing large-scale quantum processors is the realization of qubit couplings that balance interaction strength, connectivity, and mode confinement. Moreover, it is very desirable for the device elements to be detachable, allowing components to be built, tested, and replaced independently. In this work, we present a microwave quantum state router, centered on parametrically driven, Josephson-junction based three-wave mixing, that realizes all-to-all couplings among four detachable quantum modules. We demonstrate coherent exchange among all four communication modes, with an average full-iSWAP time of 764 ns and average inferred inter-module exchange fidelity of 0.969, limited by mode coherence. We also demonstrate photon transfer and pairwise entanglement between module qubits, and parallel operation of simultaneous iSWAP exchange across the router. Our router-module architecture serves as a prototype of modular quantum computer that has great potential for enabling flexible, demountable, large-scale quantum networks of superconducting qubits and cavities.

Holographic Gaussian Boson Sampling with Matrix Product States on 3D cQED Processors

“…For example, the two-mode device used to demonstrate bosonic two-qubit gates in ref , as reproduced in Figure c, can already be used to implement GBS of arbitrarily number of modes in principle using the circuits shown in Figure b. More recent demonstration of a quantum router connecting four storage modes provides all the tools necessary to implement the holographic GBS routine with added beam-splitter layers such as those shown in Figure b. In this section, we briefly review the techniques necessary to physically implement the required bosonic operations, discuss the limitations of existing hardware, and introduce a minimal construction of the 3D circuit QED device tailored for holographic GBS.…”

“…Therefore, a transmon ancilla with simultaneous dispersive coupling to multiple storage modes for their readout, such as in ref , is undesirable. Instead of designing spatially separated storage cavity modes with independent transmon ancillas as in refs and , we propose a hardware-efficient setup that satisfies all the requirements as in Figure c. The storage cavity module containing multiple modes is coupled to a three-wave mixing coupler (e.g., SNAIL) operated under the condition to minimize the fourth-order nonlinearity of the storage modes (self Kerr and cross Kerr).…”

“…Much faster gates on 100 ns scale or shorter can be implemented with parametric charge or flux drives , using novel Josephson ancilla circuitry that supports three-wave mixing processes. These ancillae, including, for example, SNAIL (Superconducting Nonlinear Asymmetric Inductive eLement), ,− RF SQUID, and ATS have been under intensive development recently. Their integration with high-coherence 3D systems has led to record beam-splitter fidelity in the range of 99.9–99.99%. , …”

Mapping Molecular Hamiltonians into Hamiltonians of Modular cQED Processors

“…A nearly quartic element can be used to implement ultrastrong cross-Kerr couplings 41 between photonic modes described by the interaction Hamiltonian, 50,51 as previously investigated for transmons. 52,53 The 4 × 4 and 8 × 8 circuits in Figure 2 can be generalized as well to include arbitrary fluxbiased Josephson circuits as a replacement for the SNAILs and the nearly quartic couplers.…”

“…As an example, Figure (b) illustrates the circuit that effectively maps the 8 × 8 Hamiltonian corresponding to a 3-qubit entangling gate. Alternatively, bilinear couplings can also be established by beams splitters, , as previously investigated for transmons. , The 4 × 4 and 8 × 8 circuits in Figure can be generalized as well to include arbitrary flux-biased Josephson circuits as a replacement for the SNAILs and the nearly quartic couplers.…”