Boosted Bell-state measurements for photonic quantum computation

Fault-tolerant Fusion-Based photonic Quantum Computing (FBQC) has emerged as a promising platform for scalable quantum computation. At its core, FBQC relies on entangling two-photon measurements called fusions, which are typically implemented using linear-optical projective Bell-State Measurements (BSMs). However, these conventional BSMs face a fundamental limitation—a success probability capped at 50%—which significantly hampers FBQC performance.

This research demonstrates a groundbreaking solution to this limitation through a technique called “boosting,” which enhances BSM success probabilities by incorporating additional quantum resources. We have successfully implemented a boosted BSM using a 4 × 4 multiport splitter and an auxiliary entangled photon pair, achieving a remarkable success probability of (69.3 ± 0.3)%, decisively surpassing the standard 50% threshold.

The fundamental architecture of FBQC centers on two key elements: entangling two-photon measurements (fusions) and compact pre-entangled resource states. Quantum operations are executed by performing fusions between photons from different resource states, with measurement basis selection determining the specific computation. Topological fault-tolerance is achieved through strategic design of resource states and fusion networks that enable error detection via parity checks.

This fiber-based implementation offers significant practical advantages over free-space alternatives, reducing experimental complexity while maintaining compatibility with existing fiber-based infrastructure. The 4 × 4 multiport interferometer design theoretically permits BSM success probabilities of up to 75%.

To evaluate real-world impact, the researchers examined this boosted BSM’s performance within an encoded six-ring fusion network—a structure specifically chosen for its inherent resilience against imperfect fusions and photon losses. Simulation results reveal dramatic improvements in system robustness: this boosted BSM tolerates individual photon-loss probability of 1.4%, compared to just 0.45% for non-boosted alternatives—representing a threefold improvement in loss tolerance.

Additionally, othisur approach significantly reduces logical error rates, marking a substantial advancement toward practical, fault-tolerant photonic quantum computing. This breakthrough brings the scientists considerably closer to realizing the full potential of photonic platforms for large-scale quantum information processing.