Label - free nanoscopy of living cells

probability of this quantum receiver did not fall below 10–4 is due to experimental limitations; in particular, the visibility of the interferometer at the beamsplitter used in the displacement operation and the detection efficiency of the singlephoton detector were major sources of imperfection. Imperfect visibility causes errors in photon counts even when a correct displacement operation is carried out, and imperfect detection efficiency causes false negatives in photon counting for some signals displaced into the nonvacuum state. Nevertheless, by employing forward error correction methods used in conventional communication systems, the error rate of 10–4 can be reduced to a nearly error-free state. This suggests some challenges for the future, including the construction of a local oscillator required for the displacement operation. Of course, other improvements may also be needed, such as speeding up the operation of the required feedback loops and field-programmable gate array technology, downsizing the size and mass of the receiver, and developing faster single-photon detectors. Moreover, if this experiment is to be conducted outside of a laboratory environment, errors caused by background light must be taken into account. ❒ Kenji Tsujino is at the Department of Physics, Tokyo Women’s Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan. e-mail: [email protected]