Figure 3: Quantum process tomography of storing a polarization state of a true single photon.
From: Single-photon-level quantum image memory based on cold atomic ensembles
(a) Schematic of the simplified experimental setup demonstrating coherence of a single photon. λ/2(λ/4): a half-wave plate (a quarter-wave plate). PBS: Glan–Taylor polarization beam splitter with the extinction ratio of 105:1. (b) Calculated real and imaginary parts of the storage process matrix χ obtained from experimental data in the Pauli operator basis {I, X, Y, Z}. For an ideal quantum memory device, the χ matrix should be peaked only at {I, I}. All data are raw, without noise correction.
