Supporting Data for the manuscript "Photonic hyperentanglement in polarisation and frequency via joint spectrum shaping"

Overview This repository contains the complete dataset supporting the experimental results presented in "Photonic hyperentanglement in polarisation and frequency via joint spectrum shaping". Refer to the manuscript for a detailed discussion of the experiment. The dataset includes: Domain engineering of the SPDC crystal Joint spectral intensity (JSI) measurements from time-of-flight spectrometry (TOFS) Biphoton interference measurements, referred here as intra-pair Hong-Ou-Mandel (HOM) interference, of the frequency-entangled state (separable in the polarisation degree of freedom). Heralded two-photon interference measurements, referred here as intra-pair Hong-Ou-Mandel (HOM) interference, of the frequency-entangled state (separable in the polarisation degree of freedom). Polarisation-resolved biphoton interference measurements of the hyperentangled state. Polarisation-resolved TOFS of the hyperentangled state. Folder structure Domain Engineering Frick_UIBKv3.csv contains the domain structure of the KTP crystal: First column: sign (orientation) of the crystal domain Second column: starting position (in um) of the domains Third column: ending position (in um) of the domains. InterPair HOM IndependentHOM_2354_Power14.0mW_Temp23.0C.csv: the file contains heralded two-photon (Hong-Ou-Mandel) interference measurements recorded without the use of spectral filtering (only lowpass filters to cut the pump laser). Measurement procedure: The relative delay between interfering photons is scanned with a translation stage, and single and coincidence events are recorded for 60 seconds for each point with a time-tagging system. Eighteen iterations of the measurement are performed. Content of the file: First row: Position of the translation stage that sets the relative delay between interfering photons in millimetres. Second row: Total four-fold coincidences, for each position, in the heralded two-photon interference. Third to sixth row: Total single counts, for each position, recorded by each channel's detector. Seventh to twenty-fourth row: Four-fold coincidences, for each position, at each iteration of the measurement. IntraPair HOM DependentHOM_2335_Power15.0mW_T80.168C.csv: the file contains intra-pair two-photon (Hong-Ou-Mandel) interference measurements recorded without the use of spectral filtering (only lowpass filters to cut the pump laser), for the frequency-entangled state (separable state in the polarisation degree of freedom). Measurement procedure: The relative delay between interfering photons is scanned with a translation stage, and single and coincidence events are recorded for 20 seconds for each point with a time-tagging system. Content of the file: First row: Position of the translation stage that sets the relative delay between interfering photons in millimetres. Second row: Total two-fold coincidences, for each position, in the two-photon interference. Third to fourth row: Total single counts, for each position, recorded by each channel's detector. Polarisation Resolved Intra Pair HOM The directory contains two folders with intra-pair Hong-Ou-Mandel (HOM) interference measurements of the hyperentangled state. Each folder is associated with a specific input polarisation Bell state, as specified in the folder name (ψ⁺ or ψ⁻). For each Bell state, measurements are recorded for different pairs of polarisation projection bases (HH, HV, VV, AA, DA, DD) at the two tomography stages connected to the outputs of the fibre beam splitter. Only the HH and DD projections are used in the results presented in the main text; the remaining bases are included for completeness. Setup geometry: Each tomography stage (j=1, 2) is placed at one output of the fibre beam splitter and consists of a quarter-wave plate, a half-wave plate, and a polarising beam splitter (PBS), yielding a transmitted (Tj) and a reflected (Rj) output channel, for a total of four single-photon detector channels. Measurement procedure: The relative temporal delay between the interfering signal and idler photons is scanned with a motorised translation stage, and single-photon counts as well as all coincidence events among the four detector channels are recorded for 20 seconds per delay point using a time-tagging system. Files' structure: File format: .csv files and one .txt file containing the measurement settings. Naming convention: Data_Measurement_Basis_<XX>.csv, where <XX> specifies the pair of polarisation projections at the two tomography stages (e.g., DA denotes a diagonal projection at stage 1 and an anti-diagonal projection at stage 2). Content of the files: Each CSV file contains a header row followed by 99 data rows with 15 columns: Position_mm — Position of the motorised translation stage in millimetres, setting the relative temporal delay between the interfering photons. Counts_T1, Counts_R1, Counts_T2, Counts_R2 — Raw single-photon counts at each of the four detector channels, where the subscript labels the tomography stage and T/R denotes the transmitted/reflected port of the corresponding PBS. Coinc_T1_T2, Coinc_T1_R1, Coinc_T1_R2, Coinc_R1_T2, Coinc_R1_R2, Coinc_T2_R2 — All six pairwise two-fold coincidence counts among the four detectors. These constitute the primary observables of the measurement. Coincidences between detectors belonging to different tomography stages (i.e., different outputs of the fibre beam splitter) — namely T1–T2, T1–R2, R1–T2, and R1–R2 — correspond to anti-bunching (cross-output) events, while coincidences between detectors within the same tomography stage — T1–R1 and T2–R2 — correspond to bunching (same-output) events. Coinc_T1_R1_T2, Coinc_T1_R1_R2, Coinc_T1_T2_R2, Coinc_R1_T2_R2 — All four three-fold coincidence counts. Coinc_T1_R1_T2_R2 — Four-fold coincidence count (all four detectors firing within the coincidence window). All count values are raw (unnormalised) photon detection events accumulated over the 20-second integration time per delay point. The higher-order (three- and four-fold) coincidences are recorded for diagnostic purposes. Polarisation Resolved TOFS The directory contains polarisation-resolved joint spectral intensity measurements of the hyperentangled state obtained via TOFS. The used Bell state is φ⁺. Measurements are recorded for different pairs of polarisation projection bases (AA, AD, AH, AL, AR, AV, DA,…) at the two tomography stages connected to the inputs of the dispersion modules of the TOFS. File structure. File format: .csv files and one .txt file containing the measurement settings. Naming convention: JSI_<XX>.csv, where <XX> specifies the pair of polarisation projections at the two tomography stages (e.g., DA denotes a diagonal projection at stage 1 and an anti-diagonal projection at stage 2). Content of the files: Each CSV file contains a two-dimensional matrix with raw, three-fold coincidence events between (1) pulsed pump trigger, (2) signal and (3) idler down-converted photons as a function of trigger-signal delay and trigger-idler delay in picoseconds (see .txt file containing the measurement settings) TOFS Contains Joint Spectral Intensity measurements for three different configurations of the pump spectral shaping: File format: .txt files. Naming convention: JSI_Sagnac_80psBin_<XX>.txt where <XX> specifies the resulting JSI (symmetric 2x2, asymmetric 2x2, asymmetric3x2) from the used shaping configuration. Content: Two-dimensional matrix with raw, three-fold coincidence events between (1) pulsed pump trigger, (2) signal and (3) idler down-converted photons as a function of trigger-signal delay and trigger-idler delay in picoseconds: Delays: first row and first column (ps). Three-folds: all other elements