LIST OF ABSTRACTS
MID-IR Quantum Scanning Microscopy with Undetected Photons
Speaker: Laurentiu Dosan
Abstract:Infrared (IR) sensing holds great promise in applications like cellular imaging and environmental sciences but faces challenges due to inefficient IR light sources and detectors. Traditional techniques, such as Raman scattering microscopy, often require high-intensity lasers that risk damaging biological samples. This work introduces quantum scanning microscopy with undetected photons, combining quantum sensing with classical scanning microscopy to address these issues. By utilizing quantum correlations under low-light conditions, the technique separates detection photons from those interacting with the sample, optimizing IR photon interaction and visible (VIS) photon detection. Compared to wide-field microscopy, it improves resolution and signal-to-noise ratio (SNR), offers a large field of view, uniform illumination, and cost reduction using a single-pixel detector. The study demonstrates a quantum light engine for scanning microscopy, achieving 40 μm spatial resolution, 36 dB SNR, and application in lipid concentration sensing across 3.3–3.4 μm wavelengths.
An efficient spin-photon interface for color centers in diamond
Speaker: Kerim Köster
Abstract: An efficient interface between quantum emitters and optical photons remains a challenge for future quantum networks. Here, we present the integration of tin-vacancy centers in diamond into an open, fiber-based microcavity. The cavity enhances light matter interaction, resulting in a Purcell enhancement of a single defect center, evidenced by a significant lifetime shortening and an increase in coherent photon collection. Furthermore, we demonstrate a deterministic coupling between the quantum emitter and single photons, observed as a dip in the transmission profile of the cavity. That quantum non-linear behavior allows to use the defect center as a single photon switch, marking a significant step towards efficient quantum networking with solid-state qubits.
Spectroscopy and coherent manipulation of REI-based organic molecular systems for quantum information applications.
Speaker: Vishnu Unni
Abstract: Rare-earth ions in solid state hosts are candidates for optically controlled spin qubits owing to their exceptional optical and spin coherence times. Recently, an organic molecular complex containing europium has shown excellent optical coherence time [1]. This opens the potential to tailor the ligand field in order to tailor the optical and spin properties in such organic complexes [2]. We further the work on the complex reported in [1] and present improved photon echo coherence time of 3 μs at 4 K. At 150 mK, we observe a narrow optical linewidth of 120 kHz using spectral hole burning (SHB) and find spin lifetime longer than an hour. Additionally, we measure the spin inhomogeneous lines of the ground state hyperfine transitions by optically detected nuclear resonance and its coherent control. Simultaneously, we screen many organic complexes [3-5] with improved optical branching ratio up to 1.3%. Using SHB, we characterize the hyperfine splitting of the ground and excited states of them and characterize the optical coherence time. The self-assembly of molecular complexes into high quality crystals is exploited to integrate them into fiber based open-access Fabry-Pérot microcavities [6]. This enhances the emission rate by the Purcell effect. These results are important steps towards single ion experiments to realize optically addressable spin qubits.
References:
[1] Serrano et al., Nature, 603, 241-246 (2022)
[2] Kuppusamy et al., Nanophotonics, 13(24), 4357-4379 (2024)
[3] S. Schlittenhardt et al, ChemPhysChem, 25 (2024)
[4] Kuppusamy et al., J. Phys. Chem. C 127, 22 (2023)
[5] Rashid Ilmi et al. J. Mater. Chem. C 8 (2020)
[6] Hunger et al., New J. Phys 12, 065038 (2010)
Heralded single photon source using hybrid non-linear cavities
Speaker: Yash Pathak
Abstract: Single-photon sources play a critical role in quantum technologies, enabling advancements in quantum communication, computation, and metrology. While quantum dots have been extensively explored for this purpose, they suffer from limitations such as spectral instability, inconsistent photon indistinguishability, rate of generation and challenges in scalability among others. To address these challenges, we present a novel approach that combines spontaneous parametric down-conversion (SPDC) in a cavity with nonlinear light-matter interactions to achieve high-purity heralded single-photon generation. Our approach leverages a hybrid cavity system that integrates SPDC with a dissipative nonlinear process—two-photon absorption (TPA) in Rubidium (85) hot vapor. This nonlinear interaction selectively suppresses higher Fock states generated as part of the squeezed state of the SPDC process by exploiting the cavity's quantum dynamics, effectively enhancing the Q factor for single-photon states. By incorporating TPA as a state-selective dissipative mechanism, we create a system where the heralded photon purity is maximized while preserving scalability and tunability. This design demonstrates the potential of hybrid cavities to surpass the limitations of conventional single-photon sources, providing a pathway toward deterministic, high-purity single-photon generation.
Photocurrent control in a light-dressed Floquet topological insulator
Speaker: Weizhe Li
Abstract: Light-dressed materials, based on Floquet engineering, offer unique opportunities to design transient band structures. Most commonly, circularly-polarized dressing light can generate topologically nontrivial nonequilibrium states known as Floquet topological insulators (FTIs) which host a variety of topological phenomena. Floquet engineering with strong optical fields opens routes to optically tunable band structures and devices for petahertz electronics. Here we demonstrate coherent control of photocurrents in light-dressed graphene. Circularly-polarized laser pulses dress the graphene into an FTI, and phase-locked second harmonic pulses drive electrons in the FTI. We map the resulting dynamics onto two-color phase dependent photocurrents. This approach allows us to measure all-optical anomalous Hall currents and photocurrent circular dichroism. Furthermore, we map out the attosecond Floquet phase by varying the twocolor phase. The coherent control of photocurrents in graphene-based FTI connects optics tools to condensed matter physics.
Deep context processing with an optoacoustic recurrent operator
Speaker: Jesus Marines
Abstract: Context passes information from the past to the present and allows to make predictions of unknown circumstances in the future. Multiple learning tasks such as speech recognition and text generation require either learning from sequences, creating the sequence itself or a combination of both. Recurrent neural networks (RNNs) access context by capturing the dynamics of sequential data, iterating information via recurrent operations. Additionally, RNNs are able to extract hidden features of its inputs, where otherwise sequential features would remain uninterpretable. However, with increasing computational complexity of RNNs, current digital processing hardware faces a bottleneck in performance and energy consumption. Neuromorphic photonic designs have shown to be a promising candidate to overcome the "von Neumann” bottleneck as they provide large speed, broad bandwidth, and little energy consumption. In this work a path towards a deep optoacoustic recurrent operator (OREO) based on stimulated Brillouin scattering is shown. OREO establishes recurrent connections between optical pulses by means of acoustic waves generated within a waveguide. We show the capabilities of OREO by using it as an acceptor to classify patterns of 3 amplitude-encoded optical pulses with an accuracy of 67%. We expect to perform more complex computations with up to 20 optical pulses at cryogenic temperatures.
An optofluidic cavity for ultrafast label-free biosensing
Speaker: Shalom Palkhivala
Abstract: Since many biochemical processes occur in aqueous environments, the sensing and characterisation of single unlabelled particles in water is of interest in fields of science such as biophysics and chemistry. We report measurements of single nanoparticles in aqueous suspension with an optofluidic fibre-based Fabry-Perot microcavity with high finesse (5 × 104 in water). By monitoring interactions between diffusing nanosystems and the optical cavity field, the dynamics of the nanosystems can be investigated. For the quantitative analysis of the diffusion dynamics of particles in a microcavity, an analytical autocorrelation function is developed which describes diffusion through an optical standing wave field. This allows us to measure the size of single unlabeled particles with diameters of down to a few nanometers.
Furthermore, the rotational dynamics of anisotropic particles are investigated by interrogating orthogonal polarization modes of the cavity. Thus, the rotation of single nanorods can be tracked with high temporal resolution (∼ 10 ns), which is orders of magnitude faster than most other state-of-the-art techniques. As an application of our sensor to the field of biosensing, we demonstrate preliminary measurements of proteins and of single DNA "origami" nanostructures.
Brillouin-based Storage of QPSK Signals With Fully Tunable Phase Retrieval
Speaker: Olivia Saffer
Introduction: Optical storage and buffer techniques are crucial for advancing all-optical networks and computing systems, of- fering higher processing speed, broader bandwidth, and lower energy consumption [1–3]. Optical information can be encoded in amplitude and phase using different frequency channels, polarization modes or even orbital angu- lar momentum modes. One such optical memory is photonic-phononic memory based on stimulated Brillouin- Mandelstam scattering (SBS) [4, 5]. It transfers information from the optical domain to slow traveling acoustic waves and back via pulsed SBS interactions. A theoretical study showed that phase encoded storage is more ro- bust against noise [6], yet this fact has not been used to its full potential. A full experimental investigation of phase using double balanced homodyne detection was only conducted recently [7]. In this work, we showcase the excellent phase retrieval of Brillouin-based memory by coherently storing and retrieving the four 2-bit quadrature phase-shift keying (QPSK) signals {00,01,10,11}, both at room temperature and at cryogenic temperatures of around 4 K [8]. We also demonstrate exceptional phase control of the readout data, which can be manipulated from 0 to 2π using all-optical methods.
Concept: The memory scheme consists of a write and a read step, involving counterpropagating optical pulses: data and control. The control pulses are downshifted from the data pulses by Ω, which corresponds to the frequency of the acoustic wave and is referred to as the Brillouin frequency shift (BFS). In the write step, the control write pulse and the data pulse are sent into the sample, a section of highly nonlinear fiber (HNLF), from opposite sides (Fig. 1(a)). The SBS process between the data pulse and the control write pulse creates a coherent acoustic wave, transferring the encoded information to the acoustic domain (Fig. 1(b)). In the read step, a control read pulse enters the fiber after a storage time t store and interacts with the previously written acoustic wave. This transfers the information from the acoustic domain back into the optical domain, at the same frequency as the original data pulse (Fig. 1(c)). Widely-used phase-key digital modulation techniques like QPSK use both in-phase (I) and quadrature (Q) components of the signal. In our experiments, we encode the states {00, 01, 10, 11} as pulses with phases {0, π ,π, 3π }. Inherent in the memory process is a global π phase shift of the readout pulses with respect 22to the original data pulses (Fig. 1(d)). However, as
Experimental Results: We showcase the phase retrieval of Brillouin-based memory by coherently storing and retrieving the four 2-bit QPSK signals {00,01,10,11} (Fig. 1(e)). At room temperature, the phase control of the readout can be achieved by offsetting the frequency of the control pulses from the BFS. At cryogenic temperatures, the access to extended storage times turns this into a two-part handle on the phase of the readout, as the storage time can additionally be used to tune the retrieved phase. Most importantly, the relative phases between QPSK signals are conserved. For a given storage time (control frequency), changing the control frequency (storage time) will add a fixed phase to all readouts.
Figure 1(f) shows the complete phase control over the retrieved phase for all four two-bit states {00, 01, 10, 11} at a fixed storage time of 30 ns. The control pulses were detuned by ΔΩ in order to achieve any arbitrary readout phase φ R ∈ [0, 2π ). In all cases, the relative phase differences between {00, 01, 10, 11} is preserved.
Our scheme uses standard telecom equipment and is therefore straightforward to integrate into existing infras- tructure. We have the ability to arbitrarily select the phase of the readout over the full phase space in a controlled manner, which is crucial for in-memory computing and signal cleaning. Notably, this phase control requires adjust- ing the control pulses alone and leaves the data unaltered. The scheme can be implemented at room temperature and cryogenic temperatures. At cryogenic temperatures, we can store the data pulses far longer, while still retain- ing the ability to coherently retrieve the information in the readout. At 3.9 K, we could coherently retrieve the data up to 140 ns after the original data was stored.
References:
- J. Bueno, S. Maktoobi, L. Froehly, I. Fischer, M. Jacquot, L. Larger, and D. Brunner, “Reinforcement learning in a large-scale photonic recurrent neural network,” Optica 5, 756–760 (2018).
- M.G.Bacvanski,S.K.Vadlamani,K.Sulimany,andD.R.Englund,“QAMNet:FastandefficientopticalQAMneural networks,” (2024). ArXiv:2409.12305.
- R. Tucker, P.-C. Ku, and C. Chang-Hasnain, “Slow-light optical buffers: capabilities and fundamental limitations,” J. Light. Technol. 23, 4046–4066 (2005). Conference Name: Journal of Lightwave Technology.
- B. Stiller, K. Jaksch, J. Piotrowski, M. Merklein, M. K. Schmidt, K. Vu, P. Ma, S. Madden, M. J. Steel, C. G. Poulton, and B. J. Eggleton, “Brillouin light storage for 100 pulse widths,” npj Nanophotonics 1, 5 (2024).
- M. Merklein, B. Stiller, K. Vu, S. J. Madden, and B. J. Eggleton, “A chip-integrated coherent photonic-phononic memory,” Nat. Commun. 8, 1–6 (2017).
- O. A. Nieves, M. D. Arnold, M. K. Schmidt, M. J. Steel, and C. G. Poulton, “Noise in Brillouin based information storage,” Opt. Express 29, 39486–39497 (2021).
- A.Geilen,S.Becker,andB.Stiller,“High-SpeedCoherentPhotonicRandom-AccessMemoryinLong-LastingSound Waves,” ACS Photonics 11, 4524–4532 (2024).
- O. Saffer, J. H. Marines Cabello, S. Becker, A. Geilen, and B. Stiller, “Brillouin-based storage of QPSK signals with fully tunable phase retrieval,” arXiv e-prints (2024).
Multi-layer optical neural networks on a single wafer
Speaker: Wenyi Li
Abstract: Recent advances in machine learning have driven demand for more energy efficient computing solutions, particularly in addressing the limitations of traditional electronic systems. We propose an integrated approach to optical neural networks (ONNs) using multiple phase masks fabricated on a single wafer. This design addresses key challenges in miniaturization and alignment while enabling efficient manufacturing through maskless fabrication. The reflective configuration processes light signals via phase-modulated pixels, each functioning as a neuron optimized through machine learning. Our method aims to achieve advanced neural network capabilities in a compact 1 cm² form factor, offering potential breakthroughs in optical computing for AI applications.
Exploiting transient resonances in nonlinear X-ray experiments
Speaker: Daniele Ronchetti
Abstract: X-ray free electron lasers (XFELs) offer the capability to produce ultra-intense (>10e12 photons) and ultra-short (few and sub-femtoseconds) x-ray pulses. The exceptional intensity of these pulses enables the massive ionization of core electronic states, resulting in the creation of transient resonances. Despite the inherent challenge posed by the ultra-fast decay time of these transient states, typically governed by the Auger-Meitner process and lasting 1-2 fs, the brief duration of XFEL pulses allows for the exploration of transient states before their decay. This leads to collective emission phenomena, such as x-ray lasing and x-ray seeded emission spectroscopy. Our investigation focuses on using transient resonances to enhance the elastic scattering factor of individual atoms. Analogous to resonant scattering, where an x-ray pulse with a wavelength matching a core-to-valence transition experiences an increased scattering factor, we utilize a core-to-core transient resonance in this context.
During an experiment at the SCS beamline of EuXFEL, we studied the scattering properties of Cu atoms irradiated by intense XFEL pulses. X-ray pulses are tuned to the Cu-Lα transition (929.7 eV) and focused down to 20 μm onto a 150 nm thick multilayer ([B4C/Cu/SiC]n) target. Photoionization followed by rapid Auger decay produces hot unbound electrons in the sample. A subsequent cascade of electron-electron collisions generates highly charged ions with severe depletion of the Cu 3d shell. In a previous transient x-ray absorption experiment of Cu [1], the authors identified an absorption peak below the natural Cu-L3 edge (932.7 eV). This peak results from the resonant 2p-3d excitation (Cu-Lαtransition) of the created 3d vacancies. Correspondingly to resonant absorption, the transient 2p-3d resonances reflect in additional resonant elastic x-ray scattering channels. This results in enhanced scattering strength of individual atoms. We demonstrated that the enhancement strongly depends on the intensity of the incoming pulse and can grow to one order of magnitude. Our findings encourage the application of the effect in innovative crystallographic methods where 3d metals may act as heavy scatterers in analogy with single-wavelength anomalous dispersion.
In this contribution, I will introduce the fundamental concept behind the enhanced resonant elastic scattering (ERES) process. Furthermore, I will present the results of the experiment conducted at the SCS beamline of the European XFEL, where we pursued ERES in a copper-based target.
[1] Mercadier L. et al., Preprint, 2023, 10.21203/rs.3.rs-2396961/v1.
Photonic engineering behind cavity-enhanced quantum light sources
Speaker: Juan José Arango Uribe
Abstract: Quantum light sources producing single-photon and entangled photon-pair states rely on light-matter interactions, but the typical strength of these interactions is weak and the relevant emission processes have spontaneous nature. As a consequence, unless carefully engineered, these sources have relatively low efficiencies. To optimize the emission, integrated optical cavities are used to enhance the brightness of the sources by intensifying the interacting fields and shaping the density of states available, so raising the photon creation probability in the desired quantum state. In addition, the direct generation of these states in an integrated environment simplify their further use as information carriers in more complex photonic quantum systems. Nevertheless, the design of these cavity-mediated interfaces leads to intricate compromises between the design parameters involved, so demanding a comprehensive analysis of the functional dependencies that ultimately affect the source efficiency. In this talk, we address some of these design challenges and report about ongoing activities at Fraunhofer IOF on the development of on-chip prototypes for quantum light sources.
