---
OA_place: publisher
_id: '21863'
abstract:
- lang: eng
text: "Atoms and photons, two things so different but yet so alike. The former,
the building block of matter, something we learn about in school and imagine it
as some tiny marbles encircled by other tinier marbles. The latter, an electromagnetic
wave, a light particle or an excitation of the electromagnetic field. Quantum
mechanics tells us about the properties of these two entities. And even if it
sounds, looks and writes counter-intuitive, it has proven right for over a century
now.\r\n\r\nIn this work, I elaborate on how we tested the laws of quantum mechanics
and how we used them learn more about the tiny building blocks of nature and the
fields they use to talk to each other. The atoms we use, are artificial. Superconducting
qubits, small electrical circuits with quantized energy levels behave like electrons
that transition between different orbitals in an atom. One of the qubits' advantages,
is also a big disadvantage. We design the circuits' energy levels and fabricate
them in a cleanroom. This allows for arbitrary spaced energy levels but in contrast
to real atoms, prevents two superconducting qubits from being alike. Still, this
qubit platform is one of the frontrunners for future quantum computing technology
and testing fundamental physics due to their scalability.\r\n\r\nWe interface
superconducting qubits, which operate in the GHz regime, with microwave photons.
We use 3D aluminum cavities as mediators between qubits and photons. The cavities
allow for non-destructive readout of the qubit state, they shield the qubits from
noise at the qubit frequency and they give us an easy way to frequency-tune these
joint systems.\r\n\r\nWe need to operate superconducting qubits and their cavities
at millikelvin temperatures in dilution refrigerators. At higher temperatures,
superconductivity suffers and even worse, the environment is filled with thermal
noise photons. This poses a fundamental limitation on the scalability of superconducting
qubit devices. Also connecting multiple devices in different fridges does not
work over room temperature links because the microwave photons used for this purpose
will be covered in noise and the quantum information they carry, will be unusable.\r\n\r\nInfrared
photons do not suffer from this noise problem since there are close to zero thermal
noise photons at their frequencies at room temperature. We cannot simply interface
superconducting devices with optical photons due their frequency mismatch and
the destructive effect of optical photons on superconductors. Therefore, we use
microwave-to-optics transducers that allow to convert microwave photons into optical
ones and vice-versa. The transducers that we use are macroscopic electro-optic
transducers using the Pockels effect in a disk-shaped Lithium Niobate whispering
gallery mode resonator. By using a strong optical pump, photons from the two frequency
domains experience a beam-splitter interaction and get converted from one to the
other.\r\n\r\nWe measure the generated optical photons using elaborate optical
setups, optical heterodyning and single photon detectors to gain knowledge about
the qubit state or the converted microwave photons. Bridging the microwave and
the optical world allows us to take advantage of both of their strengths but it
also requires deep knowledge about both of their working principles.\r\n\r\nIn
this work, we describe two experiments that our group conducted to showcase the
opportunities that arise from interfacing superconducting qubits with optical
photons but also the pitfalls, one may encounter on the way.\r\n\r\nIn the first
experiment, we managed to all-optically read out a superconducting qubit. We show
that the assignment fidelity, the probability that a measurement of the qubit
state matches the prepared state, is close to equal for all-optical, microwave-to-optics
and conventional microwave readout. We show T1 and T2 measurements for all three
readout types and give an analysis of the noise caused by the optics. Finally,
we show that the infrared light does not affect the qubit performance in a negative
way but that the heating it causes does. This is an important insight that we
used in the next experiment.\r\n\r\nThe second experiment is the upconversion
of itinerant single microwave photons to the optical domain. We show that we can
generate single microwave photons from a qubit-cavity system. We upconvert these
single photons, measure them with a single photon detector and reconstruct their
shape. By conducting a single photon Rabi measurement, we show correlations between
the microwave and the optical domain. And by thorough signal-to-noise measurements
and noise analysis, we find that we can generate single infrared photons with
high signal-to-noise ratio 5.1 and low transducer added noise (<0.012 quanta).
We show that this measurement creates a path towards entanglement of a superconducting
qubit and an optical photon and what parameters need to be improved to achieve
it. Additionally, this experiment is a proof of principle for an on-demand infrared
single photon source. More generally, it allows to link microwave quantum technology
in general to the optical domain."
acknowledged_ssus:
- _id: M-Shop
- _id: NanoFab
- _id: LifeSc
- _id: SSU
acknowledgement: "The author of this work was supported by the European Research Council
under grant no.\r\n101089099 (ERC CoG cQEO) and the European Union’s Horizon 2020
research and innovation\r\nprogram under grant no. 899354 (FETopen SuperQuLAN).\r\nThis
work was also supported by the European Research Council under grant nos. 758053\r\n(ERC
StG QUNNECT), 101248662 (ERC POC CoupledEOT), and the European Innovation\r\nCouncil
no. 101187231 (PathfinderOpen CIELO). This research was funded in whole or in part\r\nby
the Austrian Science Fund (FWF) [10.55776/F71]. For open access purposes, the author\r\nhas
applied a CC BY public copyright license to any author accepted manuscript version
arising\r\nfrom this submission.\r\niii\r\nMy co-authors in the works mentioned
later acknowledge generous support from the ISTFELLOW program, the NOMIS-ISTA fellowship,
the Horizon Europe Program HORIZONCL4-2022-QUANTUM-01-SGA via Project No. 101113946
OpenSuperQPlus100 and a DOC fellowship of the Austrian Academy of Sciences at IST
Austria.\r\n"
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Thomas
full_name: Werner, Thomas
id: 1fcd8497-dba3-11ea-a45e-c6fbd715f7c7
last_name: Werner
orcid: 0009-0001-2346-5236
citation:
ama: Werner T. Interfacing superconducting qubits with optical photons. 2026. doi:10.15479/AT-ISTA-21863
apa: Werner, T. (2026). Interfacing superconducting qubits with optical photons.
Institute of Science and Technology Austria. https://doi.org/10.15479/AT-ISTA-21863
chicago: Werner, Thomas. “Interfacing Superconducting Qubits with Optical Photons.”
Institute of Science and Technology Austria, 2026. https://doi.org/10.15479/AT-ISTA-21863.
ieee: T. Werner, “Interfacing superconducting qubits with optical photons,” Institute
of Science and Technology Austria, 2026.
ista: Werner T. 2026. Interfacing superconducting qubits with optical photons. Institute
of Science and Technology Austria.
mla: Werner, Thomas. Interfacing Superconducting Qubits with Optical Photons.
Institute of Science and Technology Austria, 2026, doi:10.15479/AT-ISTA-21863.
short: T. Werner, Interfacing Superconducting Qubits with Optical Photons, Institute
of Science and Technology Austria, 2026.
corr_author: '1'
date_created: 2026-05-12T09:04:02Z
date_published: 2026-05-12T00:00:00Z
date_updated: 2026-05-20T13:35:43Z
day: '12'
ddc:
- '530'
- '537'
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: JoFi
doi: 10.15479/AT-ISTA-21863
ec_funded: 1
file:
- access_level: open_access
checksum: a5b4d8dba83f96e955a3625c0eebee98
content_type: application/pdf
creator: twerner
date_created: 2026-05-15T15:53:57Z
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date_created: 2026-05-15T15:54:06Z
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file_size: 9370704
relation: source_file
file_date_updated: 2026-05-15T15:54:06Z
has_accepted_license: '1'
keyword:
- Superconducting qubits
- Quantum optics
- Single photons and quantum effects
- Nonlinear optics
language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
month: '05'
oa: 1
oa_version: Published Version
page: '97'
project:
- _id: bdadfa0d-d553-11ed-ba76-fb85edbd456a
grant_number: '101089099'
name: 'Cavity Quantum Electro Optics: Microwave photonics with nonclassical states'
- _id: 9B868D20-BA93-11EA-9121-9846C619BF3A
call_identifier: H2020
grant_number: '899354'
name: Quantum Local Area Networks with Superconducting Qubits
- _id: 26336814-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '758053'
name: A Fiber Optic Transceiver for Superconducting Qubits
- _id: 5b807754-ab3d-11f0-914f-ff8c34502cc9
grant_number: '101248662'
name: Integrated optical coupling for low loss electro-optic interconnects
- _id: 91aaf765-16d5-11f0-9cad-a8e7e44cccb7
grant_number: '101187231'
name: 'Cavity-Integrated Electro-Optics: Measuring, Converting and Manipulating
Microwaves with Light'
- _id: bdb108fd-d553-11ed-ba76-83dc74a9864f
grant_number: F07105
name: QUANTUM INFORMATION SYSTEMS BEYOND CLASSICAL CAPABILITIES / P5- Integration
of Superconducting Quantum Circuits
- _id: bdb7cfc1-d553-11ed-ba76-d2eaab167738
grant_number: '101080139'
name: Open Superconducting Quantum Computers (OpenSuperQPlus)
- _id: 9B861AAC-BA93-11EA-9121-9846C619BF3A
name: NOMIS Fellowship Program
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
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relation: part_of_dissertation
status: public
- id: '21870'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Johannes M
full_name: Fink, Johannes M
id: 4B591CBA-F248-11E8-B48F-1D18A9856A87
last_name: Fink
orcid: 0000-0001-8112-028X
title: Interfacing superconducting qubits with optical photons
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2026'
...
---
OA_embargo: '6'
OA_place: publisher
_id: '20798'
abstract:
- lang: eng
text: "Atom interferometers measure the relative phase shifts between coherent matter-wave
paths\r\nthat arise from interactions with external fields or inertial forces.
Due to their exceptional\r\nphase sensitivity, atom interferometers became an
essential tool for precision measurements\r\nand fundamental physics experiments,
finding applications in geodesy, gravimetry, and inertial\r\nnavigation. However,
their measurement precision is limited by quantum projection noise,\r\nwhich arises
from the Heisenberg uncertainty principle, preventing the measurement of atomic\r\nstates
with absolute precision. The generation of entanglement between the atoms offers
a\r\npath to surpass this so-called standard quantum limit, thereby enhancing
the interferometer’s\r\nphase sensitivity beyond classical measurement bounds.\r\nThis
thesis reports on the development of an atom interferometer experiment designed
to\r\nrealize cavity-mediated, squeezed Mach-Zehnder-type interferometry with
ultra-cold 87Rb atoms.\r\nThe experiment combines cavity-aided spin-squeezing
with cavity-mediated Mach-Zehnder\r\ninterferometry to demonstrate entanglement-enhanced
phase sensitivity. The experiment is\r\ncentered on a triangular optical cavity
that mediates all relevant atom-light interactions. The\r\ncavity provides optical
trapping, spin-squeezing, and Raman beam-splitter operations, enabling\r\nto perform
interferometry on a continuously trapped atomic ensemble.\r\nThe thesis elaborates
on the fundamental theoretical framework, the cavity design, and the full\r\noptical
setup, including the detailed configuration of the developed laser stabilization
methods.\r\nExperimentally, continuous loading methods were explored, resulting
in an accumulation of\r\nup to 4 × 106\r\natoms in the dipole trap within a cycle
time of 500 ms. The AC Stark shift\r\ncompensation method developed for continuous
loading was further applied for in-trap cooling\r\nto 10 µK, and optical pumping
for efficient atomic state preparation. Coherent state control\r\nwas verified
via observation of microwave-driven Rabi oscillations, and used to characterize\r\natom-cavity
coupling.\r\nThese presented results establish the experimental groundwork for
the future development of\r\ncavity-mediated, entanglement-enhanced Mach-Zehnder-type
atom interferometry."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Sebastian
full_name: Wald, Sebastian
id: 133F200A-B015-11E9-AD41-0EDAE5697425
last_name: Wald
orcid: 0000-0002-5869-1604
citation:
ama: Wald S. Atoms in a propagating-wave cavity for squeezed Mach-Zehnder atom interferometry.
2025. doi:10.15479/AT-ISTA-20798
apa: Wald, S. (2025). Atoms in a propagating-wave cavity for squeezed Mach-Zehnder
atom interferometry. Institute of Science and Technology Austria. https://doi.org/10.15479/AT-ISTA-20798
chicago: Wald, Sebastian. “Atoms in a Propagating-Wave Cavity for Squeezed Mach-Zehnder
Atom Interferometry.” Institute of Science and Technology Austria, 2025. https://doi.org/10.15479/AT-ISTA-20798.
ieee: S. Wald, “Atoms in a propagating-wave cavity for squeezed Mach-Zehnder atom
interferometry,” Institute of Science and Technology Austria, 2025.
ista: Wald S. 2025. Atoms in a propagating-wave cavity for squeezed Mach-Zehnder
atom interferometry. Institute of Science and Technology Austria.
mla: Wald, Sebastian. Atoms in a Propagating-Wave Cavity for Squeezed Mach-Zehnder
Atom Interferometry. Institute of Science and Technology Austria, 2025, doi:10.15479/AT-ISTA-20798.
short: S. Wald, Atoms in a Propagating-Wave Cavity for Squeezed Mach-Zehnder Atom
Interferometry, Institute of Science and Technology Austria, 2025.
corr_author: '1'
das_tickbox: '1'
date_created: 2025-12-11T11:48:11Z
date_published: 2025-12-11T00:00:00Z
date_updated: 2026-07-24T08:07:28Z
day: '11'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: OnHo
doi: 10.15479/AT-ISTA-20798
doi_confirm: '1'
file:
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checksum: 1be72faf529a5e8a2d03cb3d5f808b77
content_type: application/pdf
creator: swald
date_created: 2025-12-12T11:53:42Z
date_updated: 2026-06-15T22:30:03Z
embargo: 2026-06-15
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file_size: 40127601
relation: source_file
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has_accepted_license: '1'
keyword:
- entanglement-enhanced atom interferometry
- cavity QED
- spin-squeezing
- dipole trap
- quantum optics
language:
- iso: eng
license: https://creativecommons.org/licenses/by-nc/4.0/
month: '12'
oa: 1
oa_version: Published Version
page: '152'
publication_identifier:
isbn:
- 978-3-99078-075-6
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '14759'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Onur
full_name: Hosten, Onur
id: 4C02D85E-F248-11E8-B48F-1D18A9856A87
last_name: Hosten
orcid: 0000-0002-2031-204X
title: Atoms in a propagating-wave cavity for squeezed Mach-Zehnder atom interferometry
tmp:
image: /images/cc_by_nc.png
legal_code_url: https://creativecommons.org/licenses/by-nc/4.0/legalcode
name: Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
short: CC BY-NC (4.0)
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2025'
...
---
OA_place: publisher
_id: '19533'
abstract:
- lang: eng
text: "This thesis explores advancements in quantum remote sensing and non-equilibrium
phase\r\ntransitions in the microwave regime, with a focus on dissipative phase
transitions and quantumenhanced sensing.\r\nIn the first project, I experimentally
studied photon blockade breakdown as a dissipative phase\r\ntransition in a zero-dimensional
cavity-qubit system. By defining an appropriate thermodynamic\r\nlimit, we demonstrated
that the observed bistability is a genuine signature of a first-order\r\nphase
transition in this system. This work provides insight into non-equilibrium quantum\r\ndynamics
and phase transitions in driven-dissipative open quantum systems.\r\nThe second
project focuses on the experimental realization of a phase-conjugate receiver
for\r\nquantum illumination (QI), a quantum sensing protocol that enhances target
detection in noisy\r\nenvironments using entangled light. While an ideal spontaneous
parametric down-conversion\r\n(SPDC) source and receiver could, in theory, provide
up to a 6 dB advantage over classical\r\nillumination, no such ideal receiver
exists. Instead, we explore an experimental realization of a\r\nphase-conjugate
receiver for QI in the microwave regime at millikelvin temperatures using a\r\nJosephson
parametric converter (JPC) as a source of continuous-variable Gaussian entangled\r\nsignal-idler
pairs, where a maximum 3 dB advantage is theoretically achievable. We investigate\r\nkey
experimental limitations that constrain practical QI performance, contributing
to the\r\ndevelopment of quantum-enhanced sensing.\r\nAdditionally, this thesis
presents efficient digital signal processing (DSP) techniques implemented in C++
and Python in collaboration with Przemysław Zieliński and Luka Drmić. These\r\nmethods,
optimized using the Intel Integrated Performance Primitives (IPP) library, have
been\r\nessential in data acquisition, noise filtering, and correlation analysis
across multiple research\r\nprojects. Although not real-time, these DSP techniques
significantly enhance the accuracy of\r\nquantum measurements.\r\nOverall, this
thesis advances quantum-enhanced sensing by establishing the thermodynamic\r\nlimit
in a single transmon-cavity system and experimentally exploring a phase-conjugate
receiver\r\nfor QI. These findings contribute to quantum metrology, particularly
for weak signal detection\r\nand remote sensing in noisy environments.\r\n"
acknowledged_ssus:
- _id: ScienComp
- _id: M-Shop
- _id: NanoFab
- _id: LifeSc
- _id: SSU
acknowledgement: "I acknowledge the generous financial support of the Austrian Science
Fund (FWF) via BeyondC\r\n(F7105) and the European Union’s Horizon 2020 research
and innovation program (FETopen\r\nQUARTET, Grant Agreement No. 862644), which made
this research possible. I also extend\r\nmy sincere appreciation to the MIBA workshop
and the Institute of Science and Technology\r\nAustria nanofabrication facility
for their technical assistance, which was instrumental in realizing\r\nthis work."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Riya
full_name: Sett, Riya
id: 2E6D040E-F248-11E8-B48F-1D18A9856A87
last_name: Sett
orcid: 0000-0001-7641-8348
citation:
ama: Sett R. Quantum remote sensing and non-equilibrium phase transitions in the
microwave regime. 2025. doi:10.15479/AT-ISTA-19533
apa: Sett, R. (2025). Quantum remote sensing and non-equilibrium phase transitions
in the microwave regime. Institute of Science and Technology Austria. https://doi.org/10.15479/AT-ISTA-19533
chicago: Sett, Riya. “Quantum Remote Sensing and Non-Equilibrium Phase Transitions
in the Microwave Regime.” Institute of Science and Technology Austria, 2025. https://doi.org/10.15479/AT-ISTA-19533.
ieee: R. Sett, “Quantum remote sensing and non-equilibrium phase transitions in
the microwave regime,” Institute of Science and Technology Austria, 2025.
ista: Sett R. 2025. Quantum remote sensing and non-equilibrium phase transitions
in the microwave regime. Institute of Science and Technology Austria.
mla: Sett, Riya. Quantum Remote Sensing and Non-Equilibrium Phase Transitions
in the Microwave Regime. Institute of Science and Technology Austria, 2025,
doi:10.15479/AT-ISTA-19533.
short: R. Sett, Quantum Remote Sensing and Non-Equilibrium Phase Transitions in
the Microwave Regime, Institute of Science and Technology Austria, 2025.
corr_author: '1'
date_created: 2025-04-09T16:44:26Z
date_published: 2025-04-01T00:00:00Z
date_updated: 2026-08-12T08:45:39Z
day: '1'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: JoFi
doi: 10.15479/AT-ISTA-19533
doi_confirm: '1'
ec_funded: 1
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relation: source_file
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has_accepted_license: '1'
keyword:
- phase transition
- open quantum system
- phase diagram
- cavity quantum electrodynamics
- superconducting qubits
- semiclassical physics
- quantum optics
- josephson junction
- parametric converter
- phase conjugation
- quantum radar
- quantum entanglement
- correlation
- quantum sensing
language:
- iso: eng
month: '04'
oa: 1
oa_version: Published Version
page: '109'
project:
- _id: 237CBA6C-32DE-11EA-91FC-C7463DDC885E
call_identifier: H2020
grant_number: '862644'
name: Quantum readout techniques and technologies
- _id: bdb108fd-d553-11ed-ba76-83dc74a9864f
grant_number: F07105
name: QUANTUM INFORMATION SYSTEMS BEYOND CLASSICAL CAPABILITIES / P5- Integration
of Superconducting Quantum Circuits
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '18978'
relation: research_data
status: public
- id: '19280'
relation: part_of_dissertation
status: public
- id: '17183'
relation: part_of_dissertation
status: public
- id: '13117'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Johannes M
full_name: Fink, Johannes M
id: 4B591CBA-F248-11E8-B48F-1D18A9856A87
last_name: Fink
orcid: 0000-0001-8112-028X
title: Quantum remote sensing and non-equilibrium phase transitions in the microwave
regime
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: dissertation
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
year: '2025'
...
---
OA_place: repository
OA_type: green
_id: '21529'
abstract:
- lang: eng
text: 'A central challenge in the emerging field of free-electron quantum optics
is to achieve strong quantum interaction and single-photon nonlinearity between
a flying free electron and a photonic mode. Existing schemes are intrinsically
limited by electron diffraction, which puts an upper bound on the interaction
length and, therefore, on the strength of quantum coupling and nonlinearity. Here,
we propose “free-electron fibers”: effectively one-dimensional photonic systems
where free electrons copropagate with two guided modes. The first mode applies
a ponderomotive trap to the free electron, removing the limitations due to electron
diffraction. The second mode strongly couples to the guided free electron with
an enhanced coupling that is orders of magnitude larger than previous designs.
The extended interaction lengths enabled by our scheme allow for strong single-photon
nonlinearities mediated by free electrons. We predict novel quantum effects in
our system such as deterministic single-photon emission and nonlinear multimode
dynamics. Our proposal paves the way toward the realization of heralded macroscopic
nonclassical light generation, deterministic single-photon sources, and quantum
gates controlled by free-electron–photon interactions.'
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Aviv
full_name: Karnieli, Aviv
last_name: Karnieli
- first_name: Charles
full_name: Roques-Carmes, Charles
id: e2e68fc9-6505-11ef-a541-eb4e72cc3e82
last_name: Roques-Carmes
- first_name: Nicholas
full_name: Rivera, Nicholas
last_name: Rivera
- first_name: Shanhui
full_name: Fan, Shanhui
last_name: Fan
citation:
ama: Karnieli A, Roques-Carmes C, Rivera N, Fan S. Strong coupling and single-photon
nonlinearity in free-electron quantum optics. ACS Photonics. 2024;11(8):3401-3411.
doi:10.1021/acsphotonics.4c00908
apa: Karnieli, A., Roques-Carmes, C., Rivera, N., & Fan, S. (2024). Strong coupling
and single-photon nonlinearity in free-electron quantum optics. ACS Photonics.
American Chemical Society. https://doi.org/10.1021/acsphotonics.4c00908
chicago: Karnieli, Aviv, Charles Roques-Carmes, Nicholas Rivera, and Shanhui Fan.
“Strong Coupling and Single-Photon Nonlinearity in Free-Electron Quantum Optics.”
ACS Photonics. American Chemical Society, 2024. https://doi.org/10.1021/acsphotonics.4c00908.
ieee: A. Karnieli, C. Roques-Carmes, N. Rivera, and S. Fan, “Strong coupling and
single-photon nonlinearity in free-electron quantum optics,” ACS Photonics,
vol. 11, no. 8. American Chemical Society, pp. 3401–3411, 2024.
ista: Karnieli A, Roques-Carmes C, Rivera N, Fan S. 2024. Strong coupling and single-photon
nonlinearity in free-electron quantum optics. ACS Photonics. 11(8), 3401–3411.
mla: Karnieli, Aviv, et al. “Strong Coupling and Single-Photon Nonlinearity in Free-Electron
Quantum Optics.” ACS Photonics, vol. 11, no. 8, American Chemical Society,
2024, pp. 3401–11, doi:10.1021/acsphotonics.4c00908.
short: A. Karnieli, C. Roques-Carmes, N. Rivera, S. Fan, ACS Photonics 11 (2024)
3401–3411.
date_created: 2026-03-30T12:22:47Z
date_published: 2024-07-29T00:00:00Z
date_updated: 2026-04-27T10:30:37Z
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extern: '1'
external_id:
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intvolume: ' 11'
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- free electrons
- single photon nonlinearity
- electron-photon interaction
language:
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publication_identifier:
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title: Strong coupling and single-photon nonlinearity in free-electron quantum optics
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text: "About a 100 years ago, we discovered that our universe is inherently noisy,
that is, measuring any physical quantity with a precision beyond a certain point
is not possible because of an omnipresent inherent noise. We call this - the quantum
noise. Certain physical processes allow this quantum noise to get correlated in
conjugate physical variables. These quantum correlations can be used to go beyond
the potential of our inherently noisy universe and obtain a quantum advantage
over the classical applications. \r\n\r\nQuantum noise being inherent also means
that, at the fundamental level, the physical quantities are not well defined and
therefore, objects can stay in multiple states at the same time. For example,
the position of a particle not being well defined means that the particle is in
multiple positions at the same time. About 4 decades ago, we started exploring
the possibility of using objects which can be in multiple states at the same time
to increase the dimensionality in computation. Thus, the field of quantum computing
was born. We discovered that using quantum entanglement, a property closely related
to quantum correlations, can be used to speed up computation of certain problems,
such as factorisation of large numbers, faster than any known classical algorithm.
Thus began the pursuit to make quantum computers a reality. \r\n\r\nTill date,
we have explored quantum control over many physical systems including photons,
spins, atoms, ions and even simple circuits made up of superconducting material.
However, there persists one ubiquitous theme. The more readily a system interacts
with an external field or matter, the more easily we can control it. But this
also means that such a system can easily interact with a noisy environment and
quickly lose its coherence. Consequently, such systems like electron spins need
to be protected from the environment to ensure the longevity of their coherence.
Other systems like nuclear spins are naturally protected as they do not interact
easily with the environment. But, due to the same reason, it is harder to interact
with such systems. \r\n\r\nAfter decades of experimentation with various systems,
we are convinced that no one type of quantum system would be the best for all
the quantum applications. We would need hybrid systems which are all interconnected
- much like the current internet where all sorts of devices can all talk to each
other - but now for quantum devices. A quantum internet. \r\n\r\nOptical photons
are the best contenders to carry information for the quantum internet. They can
carry quantum information cheaply and without much loss - the same reasons which
has made them the backbone of our current internet. Following this direction,
many systems, like trapped ions, have already demonstrated successful quantum
links over a large distances using optical photons. However, some of the most
promising contenders for quantum computing which are based on microwave frequencies
have been left behind. This is because high energy optical photons can adversely
affect fragile low-energy microwave systems. \r\n\r\nIn this thesis, we present
substantial progress on this missing quantum link between microwave and optics
using electrooptical nonlinearities in lithium niobate. The nonlinearities are
enhanced by using resonant cavities for all the involved modes leading to observation
of strong direct coupling between optical and microwave frequencies. With this
strong coupling we are not only able to achieve almost 100\\% internal conversion
efficiency with low added noise, thus presenting a quantum-enabled transducer,
but also we are able to observe novel effects such as cooling of a microwave mode
using optics. The strong coupling regime also leads to direct observation of dynamical
backaction effect between microwave and optical frequencies which are studied
in detail here. Finally, we also report first observation of microwave-optics
entanglement in form of two-mode squeezed vacuum squeezed 0.7dB below vacuum level.
\r\nWith this new bridge between microwave and optics, the microwave-based quantum
technologies can finally be a part of a quantum network which is based on optical
photons - putting us one step closer to a future with quantum internet. "
acknowledged_ssus:
- _id: M-Shop
- _id: SSU
- _id: NanoFab
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Rishabh
full_name: Sahu, Rishabh
id: 47D26E34-F248-11E8-B48F-1D18A9856A87
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orcid: 0000-0001-6264-2162
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apa: Sahu, R. (2023). Cavity quantum electrooptics. Institute of Science
and Technology Austria. https://doi.org/10.15479/at:ista:12900
chicago: Sahu, Rishabh. “Cavity Quantum Electrooptics.” Institute of Science and
Technology Austria, 2023. https://doi.org/10.15479/at:ista:12900.
ieee: R. Sahu, “Cavity quantum electrooptics,” Institute of Science and Technology
Austria, 2023.
ista: Sahu R. 2023. Cavity quantum electrooptics. Institute of Science and Technology
Austria.
mla: Sahu, Rishabh. Cavity Quantum Electrooptics. Institute of Science and
Technology Austria, 2023, doi:10.15479/at:ista:12900.
short: R. Sahu, Cavity Quantum Electrooptics, Institute of Science and Technology
Austria, 2023.
corr_author: '1'
date_created: 2023-05-05T11:08:50Z
date_published: 2023-05-05T00:00:00Z
date_updated: 2026-04-15T06:43:26Z
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- quantum communication
- transduction
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text: "About a 100 years ago, we discovered that our universe is inherently noisy,
that is, measuring any physical quantity with a precision beyond a certain point
is not possible because of an omnipresent inherent noise. We call this - the quantum
noise. Certain physical processes allow this quantum noise to get correlated in
conjugate physical variables. These quantum correlations can be used to go beyond
the potential of our inherently noisy universe and obtain a quantum advantage
over the classical applications. \r\n\r\nQuantum noise being inherent also means
that, at the fundamental level, the physical quantities are not well defined and
therefore, objects can stay in multiple states at the same time. For example,
the position of a particle not being well defined means that the particle is in
multiple positions at the same time. About 4 decades ago, we started exploring
the possibility of using objects which can be in multiple states at the same time
to increase the dimensionality in computation. Thus, the field of quantum computing
was born. We discovered that using quantum entanglement, a property closely related
to quantum correlations, can be used to speed up computation of certain problems,
such as factorisation of large numbers, faster than any known classical algorithm.
Thus began the pursuit to make quantum computers a reality. \r\n\r\nTill date,
we have explored quantum control over many physical systems including photons,
spins, atoms, ions and even simple circuits made up of superconducting material.
However, there persists one ubiquitous theme. The more readily a system interacts
with an external field or matter, the more easily we can control it. But this
also means that such a system can easily interact with a noisy environment and
quickly lose its coherence. Consequently, such systems like electron spins need
to be protected from the environment to ensure the longevity of their coherence.
Other systems like nuclear spins are naturally protected as they do not interact
easily with the environment. But, due to the same reason, it is harder to interact
with such systems. \r\n\r\nAfter decades of experimentation with various systems,
we are convinced that no one type of quantum system would be the best for all
the quantum applications. We would need hybrid systems which are all interconnected
- much like the current internet where all sorts of devices can all talk to each
other - but now for quantum devices. A quantum internet. \r\n\r\nOptical photons
are the best contenders to carry information for the quantum internet. They can
carry quantum information cheaply and without much loss - the same reasons which
has made them the backbone of our current internet. Following this direction,
many systems, like trapped ions, have already demonstrated successful quantum
links over a large distances using optical photons. However, some of the most
promising contenders for quantum computing which are based on microwave frequencies
have been left behind. This is because high energy optical photons can adversely
affect fragile low-energy microwave systems. \r\n\r\nIn this thesis, we present
substantial progress on this missing quantum link between microwave and optics
using electrooptical nonlinearities in lithium niobate. The nonlinearities are
enhanced by using resonant cavities for all the involved modes leading to observation
of strong direct coupling between optical and microwave frequencies. With this
strong coupling we are not only able to achieve almost 100\\% internal conversion
efficiency with low added noise, thus presenting a quantum-enabled transducer,
but also we are able to observe novel effects such as cooling of a microwave mode
using optics. The strong coupling regime also leads to direct observation of dynamical
backaction effect between microwave and optical frequencies which are studied
in detail here. Finally, we also report first observation of microwave-optics
entanglement in form of two-mode squeezed vacuum squeezed 0.7dB below vacuum level.
\r\nWith this new bridge between microwave and optics, the microwave-based quantum
technologies can finally be a part of a quantum network which is based on optical
photons - putting us one step closer to a future with quantum internet. "
acknowledged_ssus:
- _id: M-Shop
- _id: SSU
- _id: NanoFab
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Rishabh
full_name: Sahu, Rishabh
id: 47D26E34-F248-11E8-B48F-1D18A9856A87
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orcid: 0000-0001-6264-2162
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apa: Sahu, R. (2023). Cavity quantum electrooptics. Institute of Science
and Technology Austria. https://doi.org/10.15479/at:ista:13175
chicago: Sahu, Rishabh. “Cavity Quantum Electrooptics.” Institute of Science and
Technology Austria, 2023. https://doi.org/10.15479/at:ista:13175.
ieee: R. Sahu, “Cavity quantum electrooptics,” Institute of Science and Technology
Austria, 2023.
ista: Sahu R. 2023. Cavity quantum electrooptics. Institute of Science and Technology
Austria.
mla: Sahu, Rishabh. Cavity Quantum Electrooptics. Institute of Science and
Technology Austria, 2023, doi:10.15479/at:ista:13175.
short: R. Sahu, Cavity Quantum Electrooptics, Institute of Science and Technology
Austria, 2023.
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