Abstract
Single-photon subtraction plays important roles in optical quantum information processing as it provides a non-Gaussian characteristic in continuous-variable quantum information. While the conventional way of implementing single-photon subtraction based on a low-reflectance beam splitter works properly for a single-mode quantum state, it is unsuitable for a multimode quantum state because a single photon is subtracted from all multiple modes without maintaining their mode coherence. Here, we experimentally implement and characterize a mode-tunable coherent single-photon subtractor based on sum-frequency generation. It can subtract a single photon exclusively from one desired time-frequency mode of light or from a coherent superposition of multiple time-frequency modes. To experimentally characterize the time-frequency modes of the single-photon subtractor, we employ quantum process tomography based on coherent states. The mode-tunable coherent single-photon subtractor will be an essential element for realizing non-Gaussian quantum networks necessary to get a quantum advantage in information processing.
- Received 7 February 2017
DOI:https://doi.org/10.1103/PhysRevX.7.031012
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Optical quantum information processing has, to date, been based on encoding quantum information in one of two complementary aspects of light: particles or waves. An emerging field of study is to combine the advantages of both of these aspects, a technique known as hybrid quantum information processing. A key quantum operation for hybrid quantum information processing is single-photon subtraction, which extracts only a single photon from a quantum state and leaves the remaining state available for further information processing. Here, we implement and characterize a single-photon subtractor that can be tuned to subtract a single photon exclusively from one desired time-frequency mode of light or coherently from multiple time-frequency modes.
We shine a femtosecond red laser light on a nonlinear crystal and generate, by the nonlinear process known as sum-frequency generation, a weak blue beam on which photons are detected. We show that we can subtract a single photon from either one time-frequency mode of light or from a coherent superposition of multiple modes. We note that successfully achieving single-photon subtraction for a multimode quantum state is much more difficult than for a single-mode state because a single photon is typically subtracted from multiple modes without preserving quantum coherence. Several outstanding questions that we solve are as follows: (i) How can one subtract a single photon exclusively from one mode among multiple modes? (ii) How can one preserve quantum coherence when a single photon is subtracted from multiple modes? (iii) How can one experimentally characterize such single-photon subtraction?
We expect that photon-level control of multimode light will be a key technique in generating multimode non-Gaussian light and in realizing scalable hybrid quantum information processing such as universal quantum computing.