---
_id: '65575'
abstract:
- lang: eng
text: For the ever-growing field of quantum information processing, large-scale,
efficient multiport interferometers serving as photonic processors are required.
In this context, the suitability of quantum walks as the interferometric base
for universal computation has been theoretically proven. In this work, we bridge
the gap between theoretical proposals and state-of-the-art experimental capabilities
by providing the recipe for the implementation of a universal photonic processor
in discrete-time quantum walks. Specifically, we present the protocol for translating
arbitrary linear transformations into the coin and step operator of a quantum
walk and map these to the experimental parameters of the established time-multiplexed
platform [A. Schreiber , Phys. Rev. Lett. , 050502 (2010)]. We show that our interface
is highly scalable and resource efficient due to the hybrid encoding consisting
of multiple degrees of freedom. Finally, we prove that our system is highly resilient
against experimental imperfections and show that it compares favorably against
existing architectures.
article_number: '054011'
author:
- first_name: Jonas
full_name: Lammers, Jonas
last_name: Lammers
- first_name: Laura
full_name: Ares, Laura
last_name: Ares
- first_name: Federico
full_name: Pegoraro, Federico
id: '88928'
last_name: Pegoraro
- first_name: Philip
full_name: Held, Philip
id: '68236'
last_name: Held
- first_name: Benjamin
full_name: Brecht, Benjamin
id: '27150'
last_name: Brecht
orcid: '0000-0003-4140-0556 '
- first_name: Jan
full_name: Sperling, Jan
id: '75127'
last_name: Sperling
orcid: 0000-0002-5844-3205
- first_name: Christine
full_name: Silberhorn, Christine
id: '26263'
last_name: Silberhorn
citation:
ama: Lammers J, Ares L, Pegoraro F, et al. Resource-efficient universal photonic
processors based on time-multiplexed hybrid architectures. Physical Review
Applied. 2026;25(5). doi:10.1103/x99y-2sms
apa: Lammers, J., Ares, L., Pegoraro, F., Held, P., Brecht, B., Sperling, J., &
Silberhorn, C. (2026). Resource-efficient universal photonic processors based
on time-multiplexed hybrid architectures. Physical Review Applied, 25(5),
Article 054011. https://doi.org/10.1103/x99y-2sms
bibtex: '@article{Lammers_Ares_Pegoraro_Held_Brecht_Sperling_Silberhorn_2026, title={Resource-efficient
universal photonic processors based on time-multiplexed hybrid architectures},
volume={25}, DOI={10.1103/x99y-2sms},
number={5054011}, journal={Physical Review Applied}, publisher={American Physical
Society (APS)}, author={Lammers, Jonas and Ares, Laura and Pegoraro, Federico
and Held, Philip and Brecht, Benjamin and Sperling, Jan and Silberhorn, Christine},
year={2026} }'
chicago: Lammers, Jonas, Laura Ares, Federico Pegoraro, Philip Held, Benjamin Brecht,
Jan Sperling, and Christine Silberhorn. “Resource-Efficient Universal Photonic
Processors Based on Time-Multiplexed Hybrid Architectures.” Physical Review
Applied 25, no. 5 (2026). https://doi.org/10.1103/x99y-2sms.
ieee: 'J. Lammers et al., “Resource-efficient universal photonic processors
based on time-multiplexed hybrid architectures,” Physical Review Applied,
vol. 25, no. 5, Art. no. 054011, 2026, doi: 10.1103/x99y-2sms.'
mla: Lammers, Jonas, et al. “Resource-Efficient Universal Photonic Processors Based
on Time-Multiplexed Hybrid Architectures.” Physical Review Applied, vol.
25, no. 5, 054011, American Physical Society (APS), 2026, doi:10.1103/x99y-2sms.
short: J. Lammers, L. Ares, F. Pegoraro, P. Held, B. Brecht, J. Sperling, C. Silberhorn,
Physical Review Applied 25 (2026).
date_created: 2026-05-07T07:00:08Z
date_updated: 2026-05-07T07:01:09Z
department:
- _id: '623'
- _id: '15'
- _id: '170'
- _id: '706'
- _id: '429'
doi: 10.1103/x99y-2sms
intvolume: ' 25'
issue: '5'
language:
- iso: eng
publication: Physical Review Applied
publication_identifier:
issn:
- 2331-7019
publication_status: published
publisher: American Physical Society (APS)
status: public
title: Resource-efficient universal photonic processors based on time-multiplexed
hybrid architectures
type: journal_article
user_id: '75127'
volume: 25
year: '2026'
...
---
_id: '66094'
abstract:
- lang: eng
text: The two-qubit controlled-not (C-NOT) gate is an essential component for gate-based
quantum circuits. In fact, its operation, combined with single qubit rotations
allows to realise any quantum circuit. Several strategies have been adopted in
order to build quantum gates. Among them, photonics offers the dual advantage
of excellent isolation from the environment and ease of manipulation at the single
qubit level. Here we adopt a scalable time-multiplexed approach in order to build
a fully reconfigurable architecture capable of implementing a post-selected C-NOT
gate with a fidelity of (93.8 ± 1.4)%. We then show how our time-multiplexed platform
can be employed to combine a C-NOT and a single qubit gate in order to generate
the four Bell states.
article_number: '5683'
article_type: original
author:
- first_name: Federico
full_name: Pegoraro, Federico
id: '88928'
last_name: Pegoraro
- first_name: Philip
full_name: Held, Philip
id: '68236'
last_name: Held
- first_name: Jonas
full_name: Lammers, Jonas
last_name: Lammers
- first_name: Benjamin
full_name: Brecht, Benjamin
id: '27150'
last_name: Brecht
orcid: '0000-0003-4140-0556 '
- first_name: Christine
full_name: Silberhorn, Christine
id: '26263'
last_name: Silberhorn
citation:
ama: Pegoraro F, Held P, Lammers J, Brecht B, Silberhorn C. Demonstration of a quantum
C-NOT gate in a time-multiplexed fully reconfigurable photonic processor. Nature
Communications. 2026;17(1). doi:10.1038/s41467-026-74861-9
apa: Pegoraro, F., Held, P., Lammers, J., Brecht, B., & Silberhorn, C. (2026).
Demonstration of a quantum C-NOT gate in a time-multiplexed fully reconfigurable
photonic processor. Nature Communications, 17(1), Article 5683.
https://doi.org/10.1038/s41467-026-74861-9
bibtex: '@article{Pegoraro_Held_Lammers_Brecht_Silberhorn_2026, title={Demonstration
of a quantum C-NOT gate in a time-multiplexed fully reconfigurable photonic processor},
volume={17}, DOI={10.1038/s41467-026-74861-9},
number={15683}, journal={Nature Communications}, publisher={Springer Science and
Business Media LLC}, author={Pegoraro, Federico and Held, Philip and Lammers,
Jonas and Brecht, Benjamin and Silberhorn, Christine}, year={2026} }'
chicago: Pegoraro, Federico, Philip Held, Jonas Lammers, Benjamin Brecht, and Christine
Silberhorn. “Demonstration of a Quantum C-NOT Gate in a Time-Multiplexed Fully
Reconfigurable Photonic Processor.” Nature Communications 17, no. 1 (2026).
https://doi.org/10.1038/s41467-026-74861-9.
ieee: 'F. Pegoraro, P. Held, J. Lammers, B. Brecht, and C. Silberhorn, “Demonstration
of a quantum C-NOT gate in a time-multiplexed fully reconfigurable photonic processor,”
Nature Communications, vol. 17, no. 1, Art. no. 5683, 2026, doi: 10.1038/s41467-026-74861-9.'
mla: Pegoraro, Federico, et al. “Demonstration of a Quantum C-NOT Gate in a Time-Multiplexed
Fully Reconfigurable Photonic Processor.” Nature Communications, vol. 17,
no. 1, 5683, Springer Science and Business Media LLC, 2026, doi:10.1038/s41467-026-74861-9.
short: F. Pegoraro, P. Held, J. Lammers, B. Brecht, C. Silberhorn, Nature Communications
17 (2026).
date_created: 2026-07-01T07:47:15Z
date_updated: 2026-07-01T08:15:21Z
department:
- _id: '288'
- _id: '623'
- _id: '15'
doi: 10.1038/s41467-026-74861-9
intvolume: ' 17'
issue: '1'
keyword:
- Photonic Quantum Computing
- Time-multiplexing
- Quantum Information
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://www.nature.com/articles/s41467-026-74861-9
oa: '1'
publication: Nature Communications
publication_identifier:
issn:
- 2041-1723
publication_status: published
publisher: Springer Science and Business Media LLC
related_material:
link:
- description: Supplementary notes to the main article
relation: supplementary_material
url: https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-026-74861-9/MediaObjects/41467_2026_74861_MOESM1_ESM.pdf
- description: Datasets and code
relation: supplementary_material
url: https://doi.org/10.5281/zenodo.20396394
status: public
title: Demonstration of a quantum C-NOT gate in a time-multiplexed fully reconfigurable
photonic processor
type: journal_article
user_id: '88928'
volume: 17
year: '2026'
...
---
_id: '45850'
abstract:
- lang: eng
text: Interference between single photons is key for many quantum optics experiments
and applications in quantum technologies, such as quantum communication or computation.
It is advantageous to operate the systems at telecommunication wavelengths and
to integrate the setups for these applications in order to improve stability,
compactness and scalability. A new promising material platform for integrated
quantum optics is lithium niobate on insulator (LNOI). Here, we realise Hong-Ou-Mandel
(HOM) interference between telecom photons from an engineered parametric down-conversion
source in an LNOI directional coupler. The coupler has been designed and fabricated
in house and provides close to perfect balanced beam splitting. We obtain a raw
HOM visibility of (93.5 ± 0.7) %, limited mainly by the source performance and
in good agreement with off-chip measurements. This lays the foundation for more
sophisticated quantum experiments in LNOI.
article_number: '23140'
author:
- first_name: Silia
full_name: Babel, Silia
id: '63231'
last_name: Babel
orcid: https://orcid.org/0000-0002-1568-2580
- first_name: Laura
full_name: Bollmers, Laura
id: '61375'
last_name: Bollmers
- first_name: Marcello
full_name: Massaro, Marcello
id: '59545'
last_name: Massaro
orcid: 0000-0002-2539-7652
- first_name: Kai Hong
full_name: Luo, Kai Hong
id: '36389'
last_name: Luo
orcid: 0000-0003-1008-4976
- first_name: Michael
full_name: Stefszky, Michael
id: '42777'
last_name: Stefszky
- first_name: Federico
full_name: Pegoraro, Federico
id: '88928'
last_name: Pegoraro
- first_name: Philip
full_name: Held, Philip
id: '68236'
last_name: Held
- first_name: Harald
full_name: Herrmann, Harald
id: '216'
last_name: Herrmann
- first_name: Christof
full_name: Eigner, Christof
id: '13244'
last_name: Eigner
orcid: https://orcid.org/0000-0002-5693-3083
- first_name: Benjamin
full_name: Brecht, Benjamin
id: '27150'
last_name: Brecht
orcid: '0000-0003-4140-0556 '
- first_name: Laura
full_name: Padberg, Laura
id: '40300'
last_name: Padberg
- first_name: Christine
full_name: Silberhorn, Christine
id: '26263'
last_name: Silberhorn
citation:
ama: Babel S, Bollmers L, Massaro M, et al. Demonstration of Hong-Ou-Mandel interference
in an LNOI directional coupler. Optics Express. 2023;31(14). doi:10.1364/oe.484126
apa: Babel, S., Bollmers, L., Massaro, M., Luo, K. H., Stefszky, M., Pegoraro, F.,
Held, P., Herrmann, H., Eigner, C., Brecht, B., Padberg, L., & Silberhorn,
C. (2023). Demonstration of Hong-Ou-Mandel interference in an LNOI directional
coupler. Optics Express, 31(14), Article 23140. https://doi.org/10.1364/oe.484126
bibtex: '@article{Babel_Bollmers_Massaro_Luo_Stefszky_Pegoraro_Held_Herrmann_Eigner_Brecht_et
al._2023, title={Demonstration of Hong-Ou-Mandel interference in an LNOI directional
coupler}, volume={31}, DOI={10.1364/oe.484126},
number={1423140}, journal={Optics Express}, publisher={Optica Publishing Group},
author={Babel, Silia and Bollmers, Laura and Massaro, Marcello and Luo, Kai Hong
and Stefszky, Michael and Pegoraro, Federico and Held, Philip and Herrmann, Harald
and Eigner, Christof and Brecht, Benjamin and et al.}, year={2023} }'
chicago: Babel, Silia, Laura Bollmers, Marcello Massaro, Kai Hong Luo, Michael Stefszky,
Federico Pegoraro, Philip Held, et al. “Demonstration of Hong-Ou-Mandel Interference
in an LNOI Directional Coupler.” Optics Express 31, no. 14 (2023). https://doi.org/10.1364/oe.484126.
ieee: 'S. Babel et al., “Demonstration of Hong-Ou-Mandel interference in
an LNOI directional coupler,” Optics Express, vol. 31, no. 14, Art. no.
23140, 2023, doi: 10.1364/oe.484126.'
mla: Babel, Silia, et al. “Demonstration of Hong-Ou-Mandel Interference in an LNOI
Directional Coupler.” Optics Express, vol. 31, no. 14, 23140, Optica Publishing
Group, 2023, doi:10.1364/oe.484126.
short: S. Babel, L. Bollmers, M. Massaro, K.H. Luo, M. Stefszky, F. Pegoraro, P.
Held, H. Herrmann, C. Eigner, B. Brecht, L. Padberg, C. Silberhorn, Optics Express
31 (2023).
date_created: 2023-07-03T14:08:36Z
date_updated: 2023-07-05T07:58:31Z
department:
- _id: '15'
- _id: '230'
- _id: '623'
- _id: '288'
doi: 10.1364/oe.484126
intvolume: ' 31'
issue: '14'
keyword:
- Atomic and Molecular Physics
- and Optics
language:
- iso: eng
publication: Optics Express
publication_identifier:
issn:
- 1094-4087
publication_status: published
publisher: Optica Publishing Group
status: public
title: Demonstration of Hong-Ou-Mandel interference in an LNOI directional coupler
type: journal_article
user_id: '63231'
volume: 31
year: '2023'
...
---
_id: '42648'
abstract:
- lang: eng
text: In real photonic quantum systems losses are an unavoidable factor limiting
the scalability to many modes and particles, restraining their application in
fields as quantum information and communication. For this reason, a considerable
amount of engineering effort has been taken in order to improve the quality of
particle sources and system components. At the same time, data analysis and collection
methods based on post-selection have been used to mitigate the effect of particle
losses. This has allowed for investigating experimentally multi-particle evolutions
where the observer lacks knowledge about the system's intermediate propagation
states. Nonetheless, the fundamental question how losses affect the behaviour
of the surviving subset of a multi-particle system has not been investigated so
far. For this reason, here we study the impact of particle losses in a quantum
walk of two photons reconstructing the output probability distributions for one
photon conditioned on the loss of the other in a known mode and temporal step
of our evolution network. We present the underlying theoretical scheme that we
have devised in order to model controlled particle losses, we describe an experimental
platform capable of implementing our theory in a time multiplexing encoding. In
the end we show how localized particle losses change the output distributions
without altering their asymptotic spreading properties. Finally we devise a quantum
civilization problem, a two walker generalisation of single particle recurrence
processes.
article_number: '034005'
article_type: original
author:
- first_name: Federico
full_name: Pegoraro, Federico
id: '88928'
last_name: Pegoraro
- first_name: Philip
full_name: Held, Philip
id: '68236'
last_name: Held
- first_name: Sonja
full_name: Barkhofen, Sonja
id: '48188'
last_name: Barkhofen
- first_name: Benjamin
full_name: Brecht, Benjamin
id: '27150'
last_name: Brecht
orcid: '0000-0003-4140-0556 '
- first_name: Christine
full_name: Silberhorn, Christine
id: '26263'
last_name: Silberhorn
citation:
ama: Pegoraro F, Held P, Barkhofen S, Brecht B, Silberhorn C. Dynamic conditioning
of two particle discrete-time quantum walks. Physica Scripta. 2023;98(3).
doi:10.1088/1402-4896/acbcaa
apa: Pegoraro, F., Held, P., Barkhofen, S., Brecht, B., & Silberhorn, C. (2023).
Dynamic conditioning of two particle discrete-time quantum walks. Physica Scripta,
98(3), Article 034005. https://doi.org/10.1088/1402-4896/acbcaa
bibtex: '@article{Pegoraro_Held_Barkhofen_Brecht_Silberhorn_2023, title={Dynamic
conditioning of two particle discrete-time quantum walks}, volume={98}, DOI={10.1088/1402-4896/acbcaa},
number={3034005}, journal={Physica Scripta}, publisher={IOP Publishing}, author={Pegoraro,
Federico and Held, Philip and Barkhofen, Sonja and Brecht, Benjamin and Silberhorn,
Christine}, year={2023} }'
chicago: Pegoraro, Federico, Philip Held, Sonja Barkhofen, Benjamin Brecht, and
Christine Silberhorn. “Dynamic Conditioning of Two Particle Discrete-Time Quantum
Walks.” Physica Scripta 98, no. 3 (2023). https://doi.org/10.1088/1402-4896/acbcaa.
ieee: 'F. Pegoraro, P. Held, S. Barkhofen, B. Brecht, and C. Silberhorn, “Dynamic
conditioning of two particle discrete-time quantum walks,” Physica Scripta,
vol. 98, no. 3, Art. no. 034005, 2023, doi: 10.1088/1402-4896/acbcaa.'
mla: Pegoraro, Federico, et al. “Dynamic Conditioning of Two Particle Discrete-Time
Quantum Walks.” Physica Scripta, vol. 98, no. 3, 034005, IOP Publishing,
2023, doi:10.1088/1402-4896/acbcaa.
short: F. Pegoraro, P. Held, S. Barkhofen, B. Brecht, C. Silberhorn, Physica Scripta
98 (2023).
date_created: 2023-03-02T09:53:59Z
date_updated: 2026-01-09T09:49:31Z
department:
- _id: '623'
- _id: '15'
- _id: '288'
- _id: '169'
doi: 10.1088/1402-4896/acbcaa
intvolume: ' 98'
issue: '3'
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://iopscience.iop.org/article/10.1088/1402-4896/acbcaa
oa: '1'
publication: Physica Scripta
publication_identifier:
issn:
- 0031-8949
- 1402-4896
publication_status: published
publisher: IOP Publishing
status: public
title: Dynamic conditioning of two particle discrete-time quantum walks
type: journal_article
user_id: '68236'
volume: 98
year: '2023'
...
---
_id: '30921'
abstract:
- lang: eng
text: Quantum walks function as essential means to implement quantum simulators,
allowing one to study complex and often directly inaccessible quantum processes
in controllable systems. In this contribution, the notion of a driven Gaussian
quantum walk is introduced. In contrast to typically considered quantum walks
in optical settings, we describe the operation of the walk in terms of a nonlinear
map rather than a unitary operation, e.g., by replacing a beam-splitter-type coin
with a two-mode squeezer, being a process that is controlled and driven by a pump
field. This opens previously unattainable possibilities for quantum walks that
include nonlinear elements as core components of their operation, vastly extending
their range of applications. A full framework for driven Gaussian quantum walks
is developed, including methods to dynamically characterize nonlinear, quantum,
and quantum-nonlinear effects. Moreover, driven Gaussian quantum walks are compared
with their classically interfering and linear counterparts, which are based on
classical coherence of light rather than quantum superpositions. In particular,
the generation and boost of highly multimode entanglement, squeezing, and other
quantum effects are studied over the duration of the nonlinear walk. Importantly,
we prove the quantumness of the evolution itself, regardless of the input state.
A scheme for an experimental realization is proposed. Furthermore, nonlinear properties
of driven Gaussian quantum walks are explored, such as amplification that leads
to an ever increasing number of correlated quantum particles, constituting a source
of new walkers during the walk. Therefore, a concept for quantum walks is proposed
that leads to—and even produces—directly accessible quantum phenomena, and that
renders the quantum simulation of nonlinear processes possible.
article_number: '042210'
article_type: original
author:
- first_name: Philip
full_name: Held, Philip
id: '68236'
last_name: Held
- first_name: Melanie
full_name: Engelkemeier, Melanie
last_name: Engelkemeier
- first_name: Syamsundar
full_name: De, Syamsundar
last_name: De
- first_name: Sonja
full_name: Barkhofen, Sonja
id: '48188'
last_name: Barkhofen
- first_name: Jan
full_name: Sperling, Jan
id: '75127'
last_name: Sperling
orcid: 0000-0002-5844-3205
- first_name: Christine
full_name: Silberhorn, Christine
id: '26263'
last_name: Silberhorn
citation:
ama: Held P, Engelkemeier M, De S, Barkhofen S, Sperling J, Silberhorn C. Driven
Gaussian quantum walks. Physical Review A. 2022;105(4). doi:10.1103/physreva.105.042210
apa: Held, P., Engelkemeier, M., De, S., Barkhofen, S., Sperling, J., & Silberhorn,
C. (2022). Driven Gaussian quantum walks. Physical Review A, 105(4),
Article 042210. https://doi.org/10.1103/physreva.105.042210
bibtex: '@article{Held_Engelkemeier_De_Barkhofen_Sperling_Silberhorn_2022, title={Driven
Gaussian quantum walks}, volume={105}, DOI={10.1103/physreva.105.042210},
number={4042210}, journal={Physical Review A}, publisher={American Physical Society
(APS)}, author={Held, Philip and Engelkemeier, Melanie and De, Syamsundar and
Barkhofen, Sonja and Sperling, Jan and Silberhorn, Christine}, year={2022} }'
chicago: Held, Philip, Melanie Engelkemeier, Syamsundar De, Sonja Barkhofen, Jan
Sperling, and Christine Silberhorn. “Driven Gaussian Quantum Walks.” Physical
Review A 105, no. 4 (2022). https://doi.org/10.1103/physreva.105.042210.
ieee: 'P. Held, M. Engelkemeier, S. De, S. Barkhofen, J. Sperling, and C. Silberhorn,
“Driven Gaussian quantum walks,” Physical Review A, vol. 105, no. 4, Art.
no. 042210, 2022, doi: 10.1103/physreva.105.042210.'
mla: Held, Philip, et al. “Driven Gaussian Quantum Walks.” Physical Review A,
vol. 105, no. 4, 042210, American Physical Society (APS), 2022, doi:10.1103/physreva.105.042210.
short: P. Held, M. Engelkemeier, S. De, S. Barkhofen, J. Sperling, C. Silberhorn,
Physical Review A 105 (2022).
date_created: 2022-04-20T06:38:07Z
date_updated: 2026-01-09T09:50:22Z
department:
- _id: '623'
- _id: '15'
- _id: '170'
- _id: '706'
- _id: '288'
- _id: '230'
- _id: '429'
- _id: '35'
doi: 10.1103/physreva.105.042210
intvolume: ' 105'
issue: '4'
language:
- iso: eng
main_file_link:
- url: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.105.042210
project:
- _id: '56'
name: 'TRR 142 - C: TRR 142 - Project Area C'
- _id: '53'
name: 'TRR 142: TRR 142'
publication: Physical Review A
publication_identifier:
issn:
- 2469-9926
- 2469-9934
publication_status: published
publisher: American Physical Society (APS)
status: public
title: Driven Gaussian quantum walks
type: journal_article
user_id: '68236'
volume: 105
year: '2022'
...