Scalable Photon-Mediated Two-Qubit Gates with Spectrally Noisy Quantum Emitters

Scalable quantum information processing requires high-fidelity two-qubit gates, yet these are often hindered by spectral diffusion and intrinsic frequency disparities between solid-state quantum emitters. The authors investigate whether a pulse-based control protocol can overcome these spectral mismatches to enable robust, photon-mediated state transfer between disparate qubits.

The authors propose the Protocol for Optimal Cavity-Enabled Gates (POCEG). For low-damping cavities, the protocol applies a sequence of pi-pulses to the qubits at the cavity frequency while periodically modulating the qubit-cavity coupling to suppress unwanted excitations. For high-damping cavities, they introduce a variation (POCEG-D) that operates in the dispersive regime, applying pulses at a frequency far-detuned from the cavity to equalize the effective frequencies of the emitters. The authors validate these protocols using both analytical average Hamiltonian theory and numerical master equation simulations.

The study demonstrates that POCEG effectively mitigates spectral noise and detuning. In the resonant regime, the protocol forces the system to behave as if the qubits were perfectly resonant, achieving state transfer fidelities above 99.9% even with significant spectral mismatch. In the dispersive regime, POCEG-D maintains high fidelity by mitigating the impact of photon loss, providing a scalable path for solid-state systems. The protocol remains robust against fluctuating noise, requiring only a modest number of pulses to reach the fault-tolerant threshold.

This work provides a practical, scalable solution to one of the most significant bottlenecks in solid-state quantum computing: the inability to perform high-fidelity operations between non-identical qubits. By enabling high-fidelity gates despite spectral noise, this protocol brings various solid-state platforms, such as quantum dots, closer to the requirements for fault-tolerant quantum computation.