Quantum Metrology beyond the Classical Limit under the Effect of Dephasing

Quantum sensors have the potential to outperform their classical counterparts. For classical sensing, the uncertainty of the estimation of the target fields scales inversely with the square root of the measurement time $T$. On the other hand, by using quantum resources, we can reduce this scaling of the uncertainty with time to $1/T$. However, as quantum states are susceptible to dephasing, it has not been clear whether we can achieve sensitivities with a scaling of $1/T$ for a measurement time longer than the coherence time. Here, we propose a scheme that estimates the amplitude of globally applied fields with the uncertainty of $1/T$ for an arbitrary time scale under the effect of dephasing. We use one-way quantum-computing-based teleportation between qubits to prevent any increase in the correlation between the quantum state and its local environment from building up and have shown that such a teleportation protocol can suppress the local dephasing while the information from the target fields keeps growing. Our method has the potential to realize a quantum sensor with a sensitivity far beyond that of any classical sensor.

Figure 1

Schematic illustration of $2L$ qubits in a ring structure to measure globally applied fields with an uncertainty scaling as $1/T$ when we use separable states. (a) Half of the qubits contain information about the target fields as a probe, while the remaining half are used as ancillary qubits for the qubit teleportation. (b) With a controlled phase gate and measurement feedforward operations, we can teleport a quantum state from the original site to the right neighboring site [30, 57].(c) After the teleportation, the measured qubit becomes the new ancilla which we initialize into $|0⟩$. (d) We repeat these steps described in (b) and (c).