Microfiber quantum sensors for protein measurement with quantum N00N state

To eliminate the problem that external stray light affects the detection result, a microfiber quantum sensor for high-precision protein measurement with two photon N00N state is demonstrated. The two-photon N00N state can eliminate the disturbance of classical interference fringes and improve its robustness. The measurement of biological sample concentration can be realized according to the change of coincidence count. The experimental results indicate that the quantum sensing system exhibits an ultra-high refractive index (RI) sensitivity of 59.4977 /RIU in the range of 1.3330–1.3384. Compared with the RI sensor using single photon "classical" interference, the RI sensitivity of the proposed sensor is improved by nearly 21 times. For the measurement of bovine serum albumin (BSA) concentration, the sensitivity of the quantum sensing system is 0.2911 /(mg/mL) with the detection limit of 0.023 mg/mL. And the measured visibility is 85.2 ± 6.7 %, which is significantly larger than the visibility threshold required to break the standard quantum limit (SQL)Vth=0.707, so the sensor exhibits ultra-high precision. By obtaining ultra-high sensitivity and precision at the low photon level, our research provides a new idea for the label-free detection of photosensitive biomolecules.