---
_id: '66665'
abstract:
- lang: eng
text: Multimode quantum light has promising applications in many areas of physics,
such as quantum communications and quantum computing. However, its multimode nature
also makes it challenging to measure its properties. Recently [I. Barakat et al.,
Optica Quantum 3, 36 (2025)], a technique for the simultaneous measurement of
squeezing of multiple broadband modes based on a phase-sensitive amplification
approach was experimentally implemented using a setup that effectively corresponds
to an SU(1,1) interferometer. Here, we aim to provide a complete theoretical analysis
of the modal structure of (generally unbalanced) SU(1,1) interferometers and a
detailed theoretical formal derivation of the framework for this technique. Utilizing
the joint Schmidt decomposition of the transfer functions, we investigate the
shape and phase profiles of the modes of the SU(1,1) interferometer and its components
[parametric down-conversion (PDC) sections] for different parametric gain regimes.
We discover a complicated interplay between the PDC modes and the modes of the
entire interferometer, and analyze it by using their overlap coefficients as a
similarity measure. Finally, we develop a rigorous processing method for the aforementioned
multimode squeezing measurement technique and discuss necessary approximations
to make this method experimentally feasible.
article_number: '033139'
article_type: original
author:
- first_name: Dennis
full_name: Scharwald, Dennis
id: '55907'
last_name: Scharwald
orcid: 0009-0007-5654-5412
- first_name: Polina
full_name: Sharapova, Polina
id: '60286'
last_name: Sharapova
citation:
ama: Scharwald D, Sharapova P. Characterization of spatial Schmidt modes in high-gain
SU(1,1) interferometers. Physical Review Research. 2026;8(3). doi:10.1103/ph64-ts39
apa: Scharwald, D., & Sharapova, P. (2026). Characterization of spatial Schmidt
modes in high-gain SU(1,1) interferometers. Physical Review Research, 8(3),
Article 033139. https://doi.org/10.1103/ph64-ts39
bibtex: '@article{Scharwald_Sharapova_2026, title={Characterization of spatial Schmidt
modes in high-gain SU(1,1) interferometers}, volume={8}, DOI={10.1103/ph64-ts39},
number={3033139}, journal={Physical Review Research}, publisher={American Physical
Society (APS)}, author={Scharwald, Dennis and Sharapova, Polina}, year={2026}
}'
chicago: Scharwald, Dennis, and Polina Sharapova. “Characterization of Spatial Schmidt
Modes in High-Gain SU(1,1) Interferometers.” Physical Review Research 8,
no. 3 (2026). https://doi.org/10.1103/ph64-ts39.
ieee: 'D. Scharwald and P. Sharapova, “Characterization of spatial Schmidt modes
in high-gain SU(1,1) interferometers,” Physical Review Research, vol. 8,
no. 3, Art. no. 033139, 2026, doi: 10.1103/ph64-ts39.'
mla: Scharwald, Dennis, and Polina Sharapova. “Characterization of Spatial Schmidt
Modes in High-Gain SU(1,1) Interferometers.” Physical Review Research,
vol. 8, no. 3, 033139, American Physical Society (APS), 2026, doi:10.1103/ph64-ts39.
short: D. Scharwald, P. Sharapova, Physical Review Research 8 (2026).
date_created: 2026-08-05T11:51:21Z
date_updated: 2026-08-12T14:29:44Z
department:
- _id: '975'
- _id: '15'
- _id: '623'
- _id: '569'
- _id: '170'
- _id: '35'
- _id: '429'
- _id: '34'
- _id: '502'
doi: 10.1103/ph64-ts39
intvolume: ' 8'
issue: '3'
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://journals.aps.org/prresearch/pdf/10.1103/ph64-ts39
oa: '1'
project:
- _id: '56'
name: TRR 142 - Project Area C
- _id: '53'
name: 'TRR 142: Maßgeschneiderte nichtlineare Photonik: Von grundlegenden Konzepten
zu funktionellen Strukturen'
- _id: '174'
name: 'TRR 142 ; TP: C10: Erzeugung und Charakterisierung von Quantenlicht in nichtlinearen
Systemen: Eine theoretische Analyse'
- _id: '52'
name: Computing Resources Provided by the Paderborn Center for Parallel Computing
publication: Physical Review Research
publication_identifier:
issn:
- 2643-1564
publication_status: published
publisher: American Physical Society (APS)
status: public
title: Characterization of spatial Schmidt modes in high-gain SU(1,1) interferometers
type: journal_article
user_id: '55907'
volume: 8
year: '2026'
...
---
_id: '67134'
abstract:
- lang: eng
text: Diffractive neural networks (DNNs) are an emerging approach for the
realization of photonic artificial intelligence, especially due to their suitability
for machine-vision applications and high-dimensional photonic information processing
at lower power consumption. However, incorporating optical nonlinear activation
functions to make DNNs a feasible alternative to their electronic counterpart
remains a challenge. Here, we investigate the inclusion of second-harmonic generation
(SHG), as one of the simplest and most efficient types of optical nonlinearities,
in DNNs. We numerically investigate the impact of SHG on the performance of classification
tasks in an all-optical nonlinear DNN. Specifically, we investigate and discuss
the essential requirements for an effective arrangement of a SHG activation in
single and multilayer DNNs. We find that the performance, in terms of classification
accuracy and class contrast, is affected strongly by the positioning of the SHG
activation. Finally, we discuss and outline the constraints for including SHG
in an experimental realization. Taking these constraints into account, we estimate
the power-related efficiency of the nonlinear DNN system. Overall, our results
provide a path towards implementing nonlinear DNNs using the SHG process.
article_number: '35794'
author:
- first_name: M.
full_name: Braasch, M.
last_name: Braasch
- first_name: A.
full_name: Kartashova, A.
last_name: Kartashova
- first_name: S.
full_name: Krasikov, S.
last_name: Krasikov
- first_name: E.
full_name: Goi, E.
last_name: Goi
- first_name: T.
full_name: Pertsch, T.
last_name: Pertsch
- first_name: S.
full_name: Saravi, S.
last_name: Saravi
citation:
ama: Braasch M, Kartashova A, Krasikov S, Goi E, Pertsch T, Saravi S. Second-harmonic
generation for enhancing the performance of diffractive neural networks. Optics
Express. 2026;34(19). doi:10.1364/oe.592467
apa: Braasch, M., Kartashova, A., Krasikov, S., Goi, E., Pertsch, T., & Saravi,
S. (2026). Second-harmonic generation for enhancing the performance of diffractive
neural networks. Optics Express, 34(19), Article 35794. https://doi.org/10.1364/oe.592467
bibtex: '@article{Braasch_Kartashova_Krasikov_Goi_Pertsch_Saravi_2026, title={Second-harmonic
generation for enhancing the performance of diffractive neural networks}, volume={34},
DOI={10.1364/oe.592467}, number={1935794},
journal={Optics Express}, publisher={Optica Publishing Group}, author={Braasch,
M. and Kartashova, A. and Krasikov, S. and Goi, E. and Pertsch, T. and Saravi,
S.}, year={2026} }'
chicago: Braasch, M., A. Kartashova, S. Krasikov, E. Goi, T. Pertsch, and S. Saravi.
“Second-Harmonic Generation for Enhancing the Performance of Diffractive Neural
Networks.” Optics Express 34, no. 19 (2026). https://doi.org/10.1364/oe.592467.
ieee: 'M. Braasch, A. Kartashova, S. Krasikov, E. Goi, T. Pertsch, and S. Saravi,
“Second-harmonic generation for enhancing the performance of diffractive neural
networks,” Optics Express, vol. 34, no. 19, Art. no. 35794, 2026, doi:
10.1364/oe.592467.'
mla: Braasch, M., et al. “Second-Harmonic Generation for Enhancing the Performance
of Diffractive Neural Networks.” Optics Express, vol. 34, no. 19, 35794,
Optica Publishing Group, 2026, doi:10.1364/oe.592467.
short: M. Braasch, A. Kartashova, S. Krasikov, E. Goi, T. Pertsch, S. Saravi, Optics
Express 34 (2026).
date_created: 2026-09-12T10:09:12Z
date_updated: 2026-09-12T10:10:04Z
department:
- _id: '975'
doi: 10.1364/oe.592467
intvolume: ' 34'
issue: '19'
language:
- iso: eng
publication: Optics Express
publication_identifier:
issn:
- 1094-4087
publication_status: published
publisher: Optica Publishing Group
status: public
title: Second-harmonic generation for enhancing the performance of diffractive neural
networks
type: journal_article
user_id: '115260'
volume: 34
year: '2026'
...
---
_id: '67133'
abstract:
- lang: eng
text: We investigated the spectral properties of squeezed light generated
via parametric down-conversion in the high-gain regime, considering both unapodized
and apodized dispersion-engineered waveguides. The gain-dependent evolution of
these states is examined starting from the low-gain regime, which includes both
highly correlated and nearly uncorrelated cases. For the unapodized configuration,
our simulated results show a monotonic increase in spectral purity with gain,
whereas for some of the apodized configuration, they exhibit a nonmonotonic dependence,
initially decreasing and then recovering at higher gain. By combining Schmidt-mode
analysis with a group-velocity-based interpretation, we explain why different
dispersion conditions exhibit distinct gain-dependent behavior, specifically that
rapid purification occurs when the pump group velocity lies between those of the
signal and idler. Our study shows that the evolution of spectral purity is governed
primarily by the underlying dispersion of the waveguide. These results demonstrate
that dispersion engineering and parametric gain can be jointly exploited to tailor
the spectral-mode structure of squeezed-light sources, enabling their optimization
for a broad range of quantum applications.
article_number: '023706'
author:
- first_name: Jatin
full_name: Kumar, Jatin
last_name: Kumar
- first_name: Aleksa
full_name: Krstić, Aleksa
last_name: Krstić
- first_name: Sina
full_name: Saravi, Sina
last_name: Saravi
- first_name: Frank
full_name: Setzpfandt, Frank
last_name: Setzpfandt
citation:
ama: Kumar J, Krstić A, Saravi S, Setzpfandt F. Toward spectral engineering of squeezed
light in high-gain parametric down-conversion. Physical Review A. 2026;114(2).
doi:10.1103/2hth-yy33
apa: Kumar, J., Krstić, A., Saravi, S., & Setzpfandt, F. (2026). Toward spectral
engineering of squeezed light in high-gain parametric down-conversion. Physical
Review A, 114(2), Article 023706. https://doi.org/10.1103/2hth-yy33
bibtex: '@article{Kumar_Krstić_Saravi_Setzpfandt_2026, title={Toward spectral engineering
of squeezed light in high-gain parametric down-conversion}, volume={114}, DOI={10.1103/2hth-yy33}, number={2023706},
journal={Physical Review A}, publisher={American Physical Society (APS)}, author={Kumar,
Jatin and Krstić, Aleksa and Saravi, Sina and Setzpfandt, Frank}, year={2026}
}'
chicago: Kumar, Jatin, Aleksa Krstić, Sina Saravi, and Frank Setzpfandt. “Toward
Spectral Engineering of Squeezed Light in High-Gain Parametric down-Conversion.”
Physical Review A 114, no. 2 (2026). https://doi.org/10.1103/2hth-yy33.
ieee: 'J. Kumar, A. Krstić, S. Saravi, and F. Setzpfandt, “Toward spectral engineering
of squeezed light in high-gain parametric down-conversion,” Physical Review
A, vol. 114, no. 2, Art. no. 023706, 2026, doi: 10.1103/2hth-yy33.'
mla: Kumar, Jatin, et al. “Toward Spectral Engineering of Squeezed Light in High-Gain
Parametric down-Conversion.” Physical Review A, vol. 114, no. 2, 023706,
American Physical Society (APS), 2026, doi:10.1103/2hth-yy33.
short: J. Kumar, A. Krstić, S. Saravi, F. Setzpfandt, Physical Review A 114 (2026).
date_created: 2026-09-12T10:08:24Z
date_updated: 2026-09-12T10:10:11Z
department:
- _id: '975'
doi: 10.1103/2hth-yy33
intvolume: ' 114'
issue: '2'
language:
- iso: eng
publication: Physical Review A
publication_identifier:
issn:
- 2469-9926
- 2469-9934
publication_status: published
publisher: American Physical Society (APS)
status: public
title: Toward spectral engineering of squeezed light in high-gain parametric down-conversion
type: journal_article
user_id: '115260'
volume: 114
year: '2026'
...