Scientists at the University of Science and Technology of China (USTC) have enhanced the performance of quantum orienteering with entangling measurements applied by way of photonic quantum walks. Quantum entanglement can manifest in both quantum states and quantum measurements. The researchers said that while there has been extensive research on entangling states, few studies of entangling measurements have been done, because entangling measurements are difficult to realize. The USTC group had previously developed a deterministic, high-fidelity method of measuring quantum entanglement via photonic quantum walks. They used this method to increase efficiency in quantum tomography and reduce the back action of quantum measurements in quantum thermodynamics. Now, they are applying this measurement method to improve the efficiency of quantum orienteering. To illustrate the challenges of quantum orienteering, here is an example: Alice wants to use quantum resources to communicate a random space direction to Bob. One possible way she can do this is to polarize a spin along the direction and send it to Bob. There is no entanglement in quantum states on Alice’s side, but entanglement emerges when Bob tries to encode the information he receives. The entanglement in quantum measurements on Bob’s end could boost the efficiency of this task, but optimal entangling measurements on parallel and antiparallel spins are difficult to realize. Schematic diagram and experimental setup for optimal orienteering with parallel and antiparallel spins. Courtesy of Tang Junfeng et al. The USTC team successfully realized such optimal entangling measurements via quantum walks. Experimental results demonstrated that entangling measurements could extract more direction information than local measurements. The fidelity of antiparallel spins showed an improvement of 3.9% over parallel spins in orienteering. The researchers believe their work demonstrates a truly nonclassical phenomenon that they attribute to entanglement in quantum measurements instead of quantum states. Their work offers a potential path to realizing entangling measurements in photonic systems. The research was published in Physical Review Letters (www.doi.org/10.1103/PhysRevLett.124.060502).
