DOI: 10.5061/dryad.1rn8pk154
title: Fast quantum interferometry at the nanometer and attosecond scales with energy-entangled photons

description: In classical optical interferometry, loss and background complicate
 achieving fast nanometer-resolution measurements with illumination at low
 light levels. Conversely, quantum two-photon interference is unaffected by
 loss and background, but nanometer-scale resolution is physically
 difficult to realize. As a solution, we enhance two-photon interference
 with highly non-degenerate energy entanglement featuring photon
 frequencies separated by 177 THz. We observe measurement resolution at the
 nanometer (attosecond) scale with only O(104) photon pairs, despite the
 presence of background and loss. Our non-destructive thickness measurement
 of a metallic thin film agrees with atomic force microscopy, which often
 achieves better resolution via destructive means. With contactless,
 non-destructive measurements in seconds or faster, our instrument enables
 metrological studies in optically challenging contexts where background,
 loss, or photosensitivity are factors.
description: # Data overview The data is organized in folders as follows: ``` figures/
 | - 1/ | | - 1b/ | | - 1c/ | | - 1d/ | - 2/ | - 3/ | - 4/ | | - 4a/ | | -
 4b/ | - 5/ | | - 5a/ | | - 5b/ | - s4/ | - s6/ | - s8/ | - s10/ | - s13/ |
 - s14/ | - s15/ | - s16/ | - s17/ | - s18/ misc/ | - ellipsometer/ ``` #
 Notes Please refer to the main manuscript and supplementary text for
 additional details regarding the data files, e.g., the measurement and
 analysis protocols utilized. Most of the data files may be readily loaded
 into a Python analysis script as pandas DataFrames. Please refer to pandas
 documentation for details. Detector naming note: The 1550a, 1550b, 810a,
 and 810b labels in data files that contain them refer to the four
 detectors used in the experiment. "1550a_810a" therefore refers
 to coincidences between the 1550a and 810a detectors. Three common types
 of "counts" appear in the data: 1. Single counts: Detection
 events on individual detectors. 2. Coincidence counts: Both types of
 coincident detection counts (coincidences and anti-coincidences). The
 individual coincidence channels are labeled such that coincidences and
 anti-coincidences may be clearly identified. 3. Accidental counts:
 Coincident detection counts resulting from uncorrelated photon pairs. File
 descriptions and uses are given below. # Figures ## 1b ### Contents ```
 accidentals\raw_acc_X.json coincidences\raw_coin_X.json ``` ###
 Description These JSON files contain the coincidence and accidental counts
 for each of the 36 projective measurements for a quantum state tomography.
 The file names are numbered from 0 through 9 (ten trials). ### Uses 1.
 Figs. 1B and S5 (density matrices) 2. Entanglement source purity,
 concurrence, and entangled singlet fraction ## 1c ### Contents ``` 1c.csv
 ``` ### Description This file contains single, coincidence, and accidental
 counts for each trombone stage position from a fringe scan. There are 13
 columns: 1. **trombone_pos:** Trombone stage position (μm) 2.
 **sing_1550a:** Single counts 3. **sing_1550b:** Single counts 4.
 **sing_810a:** Single counts 5. **sing_810b:** Single counts 6.
 **coin_1550a_810a:** Coincidence counts 7. **coin_1550a_810b:**
 Coincidence counts 8. **coin_1550b_810a:** Coincidence counts 9.
 **coin_1550b_810b:** Coincidence counts 10. **acc_1550a_810a:** Accidental
 counts 11. **acc_1550a_810b:** Accidental counts 12. **acc_1550b_810a:**
 Accidental counts 13. **acc_1550b_810b:** Accidental counts ### Uses 1.
 Fig. 1C 2. Fringe fitting (period and visibility) 3. Mean total coincident
 detections per measurement 4. Mean coincidence to accidentals ratio per
 measurement 5. Classical Fisher information (estimated resolution and
 saturation of the Cramér–Rao bound) ## 1d ### Contents ``` 1d.csv ``` ###
 Description This file contains fringe scan data for 41 coarse trombone
 positions. There are 83 columns: 1. **trombone_pos:** List of coarse
 trombone positions where fringe scans were performed (mm) 2.
 **12.647_xs:** Fringe scan at position 12.647 mm, x values (fine trombone
 position, μm) 3. **12.647_ys:** Fringe scan at position 12.647 mm, y
 values (coincidence probability) 4. ***40 more sets of columns 2-3 for 40
 additional coarse trombone positions*** ### Uses 1. Fig. 1D 2. Full width
 at half maximum of the envelope of the modulated interference dip 3.
 Maximum fringe visibility expected from envelope fit 4. Fig. S9 ## 2 ###
 Contents ``` displacements.csv reference_fringe.csv ``` ### Description
 *displacements.csv:* This file contains data for 100 trials of the
 measurement shown in Fig. 2. Each row gives the coincidence counts for a
 set displacement. There are 401 columns: 1. **set_displacements:** The set
 displacements introduced by the trombone stage (nm) 2.
 **trial_0_1550a_810a:** Coincidence counts 3. **trial_0_1550a_810b:**
 Coincidence counts 4. **trial_0_1550b_810a:** Coincidence counts 5.
 **trial_0_1550b_810b:** Coincidence counts 6. ***99 more sets of columns
 2-5 for Trials 1 through 99*** *reference_fringe.csv:* The reference
 interference fringes used to extract displacement values from the
 coincidence counts in *displacements.csv*. This file contains coincidence
 counts for each trombone stage position from a fringe scan. There are 5
 columns: 1. **trombone_pos:** Trombone stage position (μm) 2.
 **coin_1550a_810a:** Coincidence counts 3. **coin_1550a_810b:**
 Coincidence counts 4. **coin_1550b_810a:** Coincidence counts 5.
 **coin_1550b_810b:** Coincidence counts ### Uses 1. Fig. 2 ## 3 ###
 Contents ```
 3a_repeated_measurements/repeated_measurement_count_time_X.csv (10 files)
 3a_reference_fringe.csv ``` ### Description
 *repeated_measurement_count_time_X.csv:* This file contains data for 100
 trials for the data point shown in Fig. 3A corresponding to an integration
 time of X seconds. For filenames where X contains a "p"
 character, e.g., 0p1, the integration time X should be interpreted as
 containing a decimal point, e.g., 0.1 seconds. Positions x0 and x1 refer
 to the two positions on the sample being measured. Each file has 10
 columns: 1. **sample_x0_pos:** Sample x0 positions (mm) 2.
 **coin_1550a_810a_x0:** Coincidence counts 3. **coin_1550a_810b_x0:**
 Coincidence counts 4. **coin_1550b_810a_x0:** Coincidence counts 5.
 **coin_1550b_810b_x0:** Coincidence counts 6. **sample_x1_pos:** Sample x1
 positions (mm) 7. **coin_1550a_810a_x1:** Coincidence counts 8.
 **coin_1550a_810b_x1:** Coincidence counts 9. **coin_1550b_810a_x1:**
 Coincidence counts 10. **coin_1550b_810b_x1:** Coincidence counts Each
 column has 100 rows; each row represents one trial.
 *3a_reference_fringe.csv:* The reference interference fringes used to
 extract displacement values from the coincidence counts in
 *repeated_measurement_count_time_X.csv*. This file contains coincidence
 counts for each trombone stage position from a fringe scan. There are 5
 columns: 1. **trombone_pos:** Trombone stage position (μm) 2.
 **coin_1550a_810a:** Coincidence counts 3. **coin_1550a_810b:**
 Coincidence counts 4. **coin_1550b_810a:** Coincidence counts 5.
 **coin_1550b_810b:** Coincidence counts ### Uses: 1. Fig. 3A 2. Baseline
 detection rate, uncoated and coated wafer regions (Fig. 3A) 3.
 Interferometer resolution as a function of measurement time ## 4a ###
 Contents ``` 4a_classical.csv 4a_leakage.csv 4a_quantum.csv ``` ###
 Description *4a_classical.csv:* This file contains data for the classical
 interference visibility as a function of the loss half-wave plate (HWP)
 angle. There are 38 columns: 1. **loss_hwp_angles:** The angle of the loss
 HWP with respect to the angle of maximum transmission (degrees) 2.
 **count_times:** The count time per point for the fringe scan for the
 given loss HWP angle setting (s) 3. **0.0_trombone_pos:** Trombone stage
 position data for the fringe scan (HWP angle 0.0 degrees) (μm) 4.
 **0.0_sing_1550a:** Single counts (HWP angle 0.0 degrees) 5.
 **0.0_sing_1550b:** Single counts (HWP angle 0.0 degrees) 6. ***11 more
 sets of columns 3-5, for each loss HWP angle setting*** *4a_leakage.csv:*
 This file contains total coincidence and accidental counts (sum of
 1550A-810A, 1550A-810B, 1550B-810A, 1550B-810B) collected over 1000
 seconds with the entanglement source pumped at the same power as the data
 given in *4a_quantum.csv* (3 mW). The counts were collected with mode b of
 the interferometer blocked. Dividing the total counts by 1000 seconds
 yields the average per-second rate of both the 1550-nm and 810-nm photons
 leaking into the lossless port of the interferometer. There are two
 columns: 1. **coin_leakage:** Total coincidence counts 2. **acc_leakage:**
 Total accidental counts *4a_quantum.csv:* This file contains data for the
 quantum interference visibility as a function of the loss half-wave plate
 (HWP) angle. There are 110 columns: 1. **loss_hwp_angles:** The angle of
 the loss HWP with respect to the angle of maximum transmission (degrees)
 2. **count_times:** The count time per point for the fringe scan for the
 given loss HWP angle setting (s) 3. **0.0_trombone_pos:** Trombone stage
 position data for the fringe scan (HWP angle 0.0 degrees) (μm) 4.
 **0.0_coin_1550a_810a:** Coincidence counts 5. **0.0_coin_1550a_810b:**
 Coincidence counts 6. **0.0_coin_1550b_810a:** Coincidence counts 7.
 **0.0_coin_1550b_810b:** Coincidence counts 8. **0.0_acc_1550a_810a:**
 Accidental counts 9. **0.0_acc_1550a_810b:** Accidental counts 10.
 **0.0_acc_1550b_810a:** Accidental counts 11. **0.0_acc_1550b_810b:**
 Accidental counts 12. ***11 more sets of columns 3-11, for each loss HWP
 angle setting*** ### Uses 1. Fig. 4A ## 4b ### Contents ```
 classical/fringe_scan_c_background_X.csv (14 files)
 quantum/fringe_scan_q_background_0.csv (14 files) ``` ### Description
 *fringe_scan_c_background_X.csv:* These files contain data for the
 classical interference visibility as a function of background. X indicates
 the trial number. X = 0 has no external background, X = 1-13 have various
 levels of external background. Each file contains data for a single fringe
 scan (stage position and singles counts). Each file has three columns: 1.
 **trombone_pos:** Trombone stage position (μm) 2. **sing_1550a:** Single
 counts 3. **sing_1550b:** Single counts *fringe_scan_q_background_X.csv:*
 These files contain data for the quantum interference visibility as a
 function of background. X indicates the trial number. X = 0 has no
 external background, X = 1-13 have various levels of external background.
 Each file contains data for a single fringe scan (stage position, singles
 counts, and coincidence counts). Each file has nine columns: 1.
 **trombone_pos:** Trombone stage position (μm) 2. **sing_1550a:** Single
 counts 3. **sing_1550b:** Single counts 4. **sing_810a:** Single counts 5.
 **sing_810b:** Single counts 6. **coin_1550a_810a:** Coincidence counts 7.
 **coin_1550a_810b:** Coincidence counts 8. **coin_1550b_810a:**
 Coincidence counts 9. **coin_1550b_810b:** Coincidence counts ### Uses 1.
 Fig. 4B ## 5a ### Contents ```
 test_sample_classical/test_sample_scan_c_X.csv (100 files)
 test_sample_quantum/test_sample_scan_q_X.csv (100 files)
 test_sample_vis_scan_c.csv test_sample_vis_scan_q.csv ``` ### Description
 These files contain measurement data for the test sample (5-nm thickness).
 *test_sample_classical/test_sample_scan_c_X.csv:* Data for sample scan
 trial X (X goes from 0 through 99), using classical interference. Each
 file records single counts as a function of sample position. Each file has
 three columns: 1. **sample_pos:** Sample positions (mm) 2. **sing_1550a:**
 Single counts 3. **sing_1550b:** Single counts
 *test_sample_quantum/test_sample_scan_q_X.csv:* Data for sample scan trial
 X (X goes from 0 through 99), using quantum interference. Each file
 records coincidence counts as a function of sample position. Each file has
 five columns: 1. **sample_pos:** Sample positions (mm) 2.
 **coin_1550a_810a:** Coincidence counts 3. **coin_1550a_810b:**
 Coincidence counts 4. **coin_1550b_810a:** Coincidence counts 5.
 **coin_1550b_810b:** Coincidence counts *test_sample_vis_scan_c.csv:*
 Classical interference fringe scan data for sample positions 6.5 mm and
 13.5 mm. There are 7 columns: 1. **sample_pos:** Sample positions (mm) 2.
 **6.5_trombone_pos:** Trombone stage position data (μm) for the fringe
 scan at sample position 6.5 mm 3. **6.5_sing_1550a:** Single counts data
 for the fringe scan at sample position 6.5 mm 4. **6.5_sing_1550b:**
 Single counts data for the fringe scan at sample position 6.5 mm 5.
 **13.5_trombone_pos:** Trombone stage position data (μm) for the fringe
 scan at sample position 13.5 mm 6. **13.5_sing_1550a:** Single counts data
 for the fringe scan at sample position 13.5 mm 7. **13.5_sing_1550b:**
 Single counts data for the fringe scan at sample position 13.5 mm
 *test_sample_vis_scan_q.csv:* Quantum interference fringe scan data for
 multiple sample positions. There are 76 columns: 1. **sample_pos:** Sample
 positions (mm) 2. **6.5_trombone_pos:** Trombone stage position data (μm)
 for the fringe scan at sample position 6.5 mm 3. **6.5_coin_1550a_810a:**
 Coincidence counts data for the fringe scan at sample position 6.5 mm 4.
 **6.5_coin_1550a_810b:** Coincidence counts data for the fringe scan at
 sample position 6.5 mm 5. **6.5_coin_1550b_810a:** Coincidence counts data
 for the fringe scan at sample position 6.5 mm 6. **6.5_coin_1550b_810b:**
 Coincidence counts data for the fringe scan at sample position 6.5 mm 7.
 ***14 more sets of columns 2-6, for each sample position*** ### Uses 1.
 Fig. 5A 2. Test sample thickness measurement, quantum 3. Test sample
 thickness measurement, classical 4. Change in interference visibility from
 uncoated to coated regions of test sample, quantum and classical 5.
 Quantum probe transmission through test sample (coated region) 6. Fitted
 beam 1/e^2 diameter ## 5b ### Contents ``` afm_image.ibw afm_profile.txt
 ``` ### Description *afm_image.ibw:* Data file for the image shown in the
 top panel of Fig. 5B. Tilt correction applied. May be opened with Gwyddion
 (free and open-source software). *afm_profile.txt:* x-y coordinates for
 the bottom panel plot. Obtained from *afm_image.ibw* The images shown in
 Fig. 5B are flipped around the vertical axis for visual clarity purposes.
 ### Uses 1. Fig. 5B 2. Test sample thickness measurement, atomic force
 microscope (AFM) ## s4 ### Contents ``` 532nm_spectrum.asc
 810nm_spectrum.asc ``` ### Description *532nm_spectrum.asc:* Spectrum for
 the 532-nm pump laser *810nm_spectrum.asc:* Spectrum for the 810-nm
 photons Both files have two columns: 1. **[No Title]**: Wavelength (nm) 2.
 **[No Title]**: Intensity (a.u.) ### Uses 1. Fig. S4 2. Photon center
 wavelengths and bandwidths ## s6 ### Contents ``` s6.csv ``` ###
 Description Data file with coincidence counts as a function of time. There
 are five columns: 1. **timestamp:** In the format YYYY-MM-DD HH:MM:SS
 (24-hour clock) 2. **coin_1550a_810a:** Coincidence counts 3.
 **coin_1550a_810b:** Coincidence counts 4. **coin_1550b_810a:**
 Coincidence counts 5. **coin_1550b_810b:** Coincidence counts ### Uses 1.
 Fig. S6 ## s8 ### Contents ``` s8.csv ``` ### Description Knife-edge scan
 data. There are 12 columns: 1. **z0_x_displacement** 2. **z0_x_scan_810**
 3. **z0_x_scan_1550** 4. **z0_y_displacement** 5. **z0_y_scan_810** 6.
 **z0_y_scan_1550** 7. **z1_x_displacement** 8. **z1_x_scan_810** 9.
 **z1_x_scan_1550** 10. **z1_y_displacement** 11. **z1_y_scan_810** 12.
 **z1_y_scan_1550** The “displacement” columns indicate the knife-edge
 displacement (in mm). The “scan” columns give the corresponding normalized
 power for the indicated wavelength (810 nm or 1550 nm). X and Y indicate
 the scan direction (horizontal and vertical, respectively). z0 and z1
 indicate the longitudinal positions (z0 = 0 mm, z1 = 45 mm). ### Uses 1.
 Fig. S8 2. Mean 1/e^2 radii of the 1550-nm and 810-nm beams ## s10 ###
 Contents ``` fringe_scan_1mW.csv fringe_scan_2mW.csv fringe_scan_3mW.csv
 fringe_scan_4mW.csv ``` ### Description Fringe scan data for pump powers
 of 1, 2, 3, and 4 mW. Each file contains single, coincidence, and
 accidental counts for each trombone stage position from a fringe scan.
 Each file has 13 columns: 1. **trombone_pos:** Trombone stage position
 (μm) 2. **sing_1550a:** Single counts 3. **sing_1550b:** Single counts 4.
 **sing_810a:** Single counts 5. **sing_810b:** Single counts 6.
 **coin_1550a_810a:** Coincidence counts 7. **coin_1550a_810b:**
 Coincidence counts 8. **coin_1550b_810a:** Coincidence counts 9.
 **coin_1550b_810b:** Coincidence counts 10. **acc_1550a_810a:** Accidental
 counts 11. **acc_1550a_810b:** Accidental counts 12. **acc_1550b_810a:**
 Accidental counts 13. **acc_1550b_810b:** Accidental counts ### Uses 1.
 Figure S10 2. Detected pair rate of at least 150,000 per second
 (interferometer) 3. Coincidence to accidental ratio, 1 mW and 3 mW ## s13
 ### Contents ``` s13.csv ``` ### Description Knife-edge scan data. There
 are 12 columns: 1. **x_displacement:** Knife-edge displacements, x-scan
 (mm) 2. **x_sing_1550a:** Single counts 3. **x_sing_1550b:** Single counts
 4. **x_sing_810a:** Single counts 5. **x_sing_810b:** Single counts 6.
 **y_displacement:** Knife-edge displacements, y-scan (mm) 7.
 **y_sing_1550a:** Single counts 8. **y_sing_1550b:** Single counts 9.
 **y_sing_810a:** Single counts 10. **y_sing_810b:** Single counts X and Y
 indicate the scan direction (horizontal and vertical, respectively). ###
 Uses 1. Fig. S13 2. Mean effective probe beam 1/e^2 diameter ## s14 ###
 Contents ``` calibration_sample_quantum/calibration_sample_scan_q_X.csv
 (100 files) calibration_sample_vis_scan_c.csv
 calibration_sample_vis_scan_q.csv ``` ### Description These files contain
 measurement data for the calibration sample (50-nm thickness).
 *calibration_sample_quantum/calibration_sample_scan_q_X.csv:* Data for
 sample scan trial X (X goes from 0 through 99), using quantum
 interference. Each file records coincidence counts as a function of sample
 position. Each file has five columns: 1. **sample_pos:** Sample positions
 (mm) 2. **coin_1550a_810a:** Coincidence counts 3. **coin_1550a_810b:**
 Coincidence counts 4. **coin_1550b_810a:** Coincidence counts 5.
 **coin_1550b_810b:** Coincidence counts
 *calibration_sample_vis_scan_c.csv:* Classical interference fringe scan
 data for sample positions 6.5 mm and 13.5 mm. There are 7 columns: 1.
 **sample_pos:** Sample positions (mm) 2. **12.0_trombone_pos:** Trombone
 stage position data (μm) for the fringe scan at sample position 12.0 mm 3.
 **12.0_sing_1550a:** Single counts data for the fringe scan at sample
 position 12.0 mm 4. **12.0_sing_1550b:** Single counts data for the fringe
 scan at sample position 12.0 mm 5. **5.5_trombone_pos:** Trombone stage
 position data (μm) for the fringe scan at sample position 5.5 mm 6.
 **5.5_sing_1550a:** Single counts data for the fringe scan at sample
 position 5.5 mm 7. **5.5_sing_1550b:** Single counts data for the fringe
 scan at sample position 5.5 mm *calibration_sample_vis_scan_q.csv:*
 Quantum interference fringe scan data for multiple sample positions. There
 are 71 columns: 1. **sample_pos:** Sample positions (mm) 2.
 **12.0_trombone_pos:** Trombone stage position data (μm) for the fringe
 scan at sample position 12.0 mm 3. **12.0_coin_1550a_810a:** Coincidence
 counts data for the fringe scan at sample position 12.0 mm 4.
 **12.0_coin_1550a_810b:** Coincidence counts data for the fringe scan at
 sample position 12.0 mm 5. **12.0_coin_1550b_810a:** Coincidence counts
 data for the fringe scan at sample position 12.0 mm 6.
 **12.0_coin_1550b_810b:** Coincidence counts data for the fringe scan at
 sample position 12.0 mm 7. ***13 more sets of columns 2-6, for each sample
 position*** ### Uses 1. Fig. S14 2. Quantum probe transmission through
 calibration sample (coated region) 3. Change in interference visibility
 from uncoated to coated regions of calibration sample, quantum and
 classical 4. Effective film refractive index, quantum probe ## s15 ###
 Contents ``` scanning_stylus_image.bcrf scanning_stylus_profiles.txt ```
 ### Description *scanning_stylus_image.bcrf:* Data file used to generate
 the profiles in *scanning_stylus_profiles.txt*. Tilt correction not
 applied. Note that a portion of the image is empty (no data). May be
 opened with Gwyddion (free and open-source software).
 *scanning_stylus_profiles.txt:* Data for individual profiles obtained from
 *scanning_stylus_image.bcrf* (after tilt correction). There are 10
 columns: 1. **[Header rows]:** X coordinates for horizontal profile 1 (m)
 2. **[Header rows]:** Y coordinates for horizontal profile 1 (m) 3.
 ***Four more sets of X-Y coordinates for horizontal profiles 2 through
 5*** ### Uses 1. Fig. S15 ## s16 ### Contents ``` profiles\profile_X.csv
 3d_optical_profilometer_image_height.csv 3d_optical_profilometer_image.cag
 3d_optical_profilometer_image.xlsx ``` ### Description *profile_X.csv:* x
 and z coordinates (in μm) for horizontal profile X (for six profiles
 numbered 1 through 6). Obtained from *3d_optical_profilometer_image.cag*.
 *3d_optical_profilometer_image_height.csv:* Height data exported from
 *3d_optical_profilometer_image.cag*. *3d_optical_profilometer_image.cag:*
 Data file used to generate the profiles in the *profiles* folder. Requires
 MultiFileAnalyzer software (Keyence Corporation). Proprietary software.
 *3d_optical_profilometer_image.xlsx:* Image files exported from
 *3d_optical_profilometer_image.cag*. ### Uses 1. Fig. S16 ## s17 ###
 Contents ``` s17.csv ``` ### Description This file contains single and
 coincidence counts for each trombone stage position from a fringe scan.
 There are 9 columns: 1. **trombone_pos:** Trombone stage position (μm) 2.
 **sing_1550a:** Single counts 3. **sing_1550b:** Single counts 4.
 **sing_810a:** Single counts 5. **sing_810b:** Single counts 6.
 **coin_1550a_810a:** Coincidence counts 7. **coin_1550a_810b:**
 Coincidence counts 8. **coin_1550b_810a:** Coincidence counts 9.
 **coin_1550b_810b:** Coincidence counts ### Uses 1. Fig. S17 ## s18 ###
 Contents ``` s18.csv ``` ### Description This file contains single,
 coincidence, and accidental counts for each trombone stage position from a
 fringe scan. There are 13 columns: 1. **trombone_pos:** Trombone stage
 position (μm) 2. **sing_1550a:** Single counts 3. **sing_1550b:** Single
 counts 4. **sing_810a:** Single counts 5. **sing_810b:** Single counts 6.
 **coin_1550a_810a:** Coincidence counts 7. **coin_1550a_810b:**
 Coincidence counts 8. **coin_1550b_810a:** Coincidence counts 9.
 **coin_1550b_810b:** Coincidence counts 10. **acc_1550a_810a:** Accidental
 counts 11. **acc_1550a_810b:** Accidental counts 12. **acc_1550b_810a:**
 Accidental counts 13. **acc_1550b_810b:** Accidental counts ### Uses 1.
 Fig. S18 2. Fringe fitting (period and visibility) 3. Mean total
 coincident detections per measurement 4. Classical Fisher information
 (estimated resolution and saturation of the Cramér–Rao bound) # Misc ##
 ellipsometer ### Contents ``` calibration_ellipsometer.dat ``` ###
 Description This file contains ellipsometer measurement data for the
 calibration sample (50-nm thickness). The file was generated by WVASE
 software (J.A. Woollam Co., Inc.). In addition to the header rows with
 measurement details, there are 6 columns: 1. **[No title]:** Wavelength
 (nm) 2. **[No title]:** Angle of incidence (degrees) 3. **[No title]:**
 Psi (degrees) 4. **[No title]:** Delta (degrees) 5. **[No title]:**
 Standard deviation, Psi (degrees) 6. **[No title]:** Standard deviation,
 Delta (degrees) ### Uses 1. Nickel film refractive index, 1550 nm