Abstract
Quantum technologies harness the intrinsic nature of quantum physics to beat limitations of classical
methods. Recently, the application of quantum entanglement to metrology has attracted much attention.
Quantum optical coherence tomography (QOCT) using two-photon interference between entangled
photon pairs can overcome certain problems with classical optical coherence tomography (OCT). As the
resolution of OCT becomes higher, degradation of the resolution due to dispersion becomes more
critical. Here we show our work on the realization of 0.54 μm resolution two-photon interference, which
surpasses the current record resolution 0.75 μm for OCT. In addition, the resolution for QOCT showed
almost no change even when a 1-mm-thick water was inserted in the path of the interferometer. The
results presented here represent a breakthrough for the realization of ultrahigh-resolution quantum
metrology. Our work will open up possibilities for medical and biological applications.
