Quantum communication between remote chips is essential for realizing large-scale superconducting quantum computers. For such communication, itinerant microwave photons propagating through transmission lines offer a promising approach. However, demonstrations to date have relied on frequency-tunable circuit elements to compensate for fabrication-related parameter variations between sender and receiver devices, introducing control complexity and limiting scalability. In this work, we demonstrate deterministic quantum state transfer and remote entanglement generation between fixed-frequency superconducting qubits on separate chips. To compensate for the sender-receiver mismatch, we employ a frequency-tunable photon-generation technique which enables us to adjust the photon frequency without modifying circuit parameters. To enhance the frequency tunability, we implement broadband transfer resonators composed of two coupled coplanar-waveguide resonators, achieving a bandwidth of more than 100 MHz. This broadband design enables successful quantum communication across a 30-MHz range of photon frequencies between the remote qubits. Quantum process tomography reveals state transfer fidelities of around 79% and Bell-state fidelities of around 73% across the full frequency range. Our approach avoids the complexity of the control lines and noise channels, providing a flexible pathway toward scalable quantum networks.
Cavity-mediated interconnects are a promising platform for scaling modular quantum computers by enabling highfidelity inter-chip quantum state transmission and entanglement generation. In this work, we first model the dynamics of deterministic inter-chip quantum state transfer using the Stimulated Raman Adiabatic Passage (STIRAP) protocol, analyzing fidelity loss mechanisms under experimentally achievable qubitcavity coupling and decoherence parameters. We then extend the NetSquid simulator, typically used for simulating longrange quantum communication networks, to support cavity-based communication channels for mediating inter-chip state transfer and entanglement generation. We model cavities as amplitude damping channels parameterized by physical system characteristics; cavity decay rate
κand qubit-cavity coupling strength
g, and analyze the impact of intrinsic qubit decoherence factors dictated by
T1and
T2times. Our simulations accurately represent the system's dynamics in both strong and weak coupling regimes, and identify critical trade-offs between fidelity, latency, and noise factors. The proposed framework supports faithful modeling and scalable simulation of modular architectures, and provides insights into design optimization for practical quantum network implementations.
We demonstrate the efficient modulation of flux-tunable superconducting resonators (FTRs) using flip-chip or on-chip-based input coils. The FTRs we use are aluminum-based quarter-wave coplanar waveguide resonators terminated with 100um or 200um-wide square loop dc superconducting quantum interference devices (SQUIDs) employing 1um-sized Josephson junctions. We employ SQUIDs with a geometric loop inductance of up to 0.7nH to increase the flux transfer efficiency. The geometric inductance of the SQUID results in a non-zero screening parameter
βL, whose branch switching effect is mitigated by using asymmetric junctions. We achieve flux modulation of the FTRs by more than one GHz and flux responsivities of up to tens of GHz/
Φ0 with uA-scale on-chip currents. We compare flip-chip with on-chip input-coil-based flux modulation, where the former is realized through galvanically connected and closely spaced chips, while the latter is achieved through superconducting air-bridge connections. We achieve a flux-transfer efficiency from the input coil to the SQUID loop of up to 20%. Our work paves the way for efficient low current flux modulation of FTRs and sensitive measurement of flux signals.