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 fully characterize the implemented single-photon subtractions, 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.
Highlights
Optical quantum information processing can be classified mainly into two approaches depending on the encoding of quantum information: One is based on continuous electric-field quadratures, and the other is based on discrete photon numbers
We start by implementing the single-photon subtraction for the HG0 mode by sending a gate beam in the HG0 mode
We could readily tune the time-frequency modes of singlephoton subtraction by adjusting the spectral modes of the gate beam, which does not require a physical reconstruction of a mode-coupling device [6,7,8,9]
Summary
Optical quantum information processing can be classified mainly into two approaches depending on the encoding of quantum information: One is based on continuous electric-field quadratures ( referred to as continuous-variable quantum information), and the other is based on discrete photon numbers (discrete-variable quantum information). A new approach to combine both advantages has attracted much attention; it is called hybrid quantum information processing [10]. One of the fundamental operations for the hybrid approach is single-photon subtraction, mathematically described by the annihilation operator a.
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