arXiv subjects

Michał Karpiński

Publications and source records attributed to Michał Karpiński.

At least 19 recordsLinked to original sources

arXiv2026

Observation of Photon Bunching in Broadband Multimode Thermal Light Enabled by Temporal Imaging

Photons emitted by incoherent sources exhibit temporal bunching, a fundamental manifestation of Bose-Einstein statistics first observed by Hanbury Brown and Twiss (HBT). While intensity correlation measurements originated in astronomy and are now central across quantum technologies, biophysics, and spectroscopy, observing temporal bunching in broadband thermal light remains limited by detector temporal resolution. Conventional approaches - such as streak cameras or optical upconversion - introduce severe trade-offs in efficiency, bandwidth, or setup versatility. Here, we propose and demonstrate a third route: pre-detection temporal magnification of the optical field prior to measuring its intensity autocorrelation function in a conventional HBT setup. Using an electro-optic time lens with a temporal magnification of 660, we resolve the temporal intensity autocorrelation of broadband thermal light generated via non-degenerate spontaneous parametric down-conversion with a bandwidth of 250 GHz. This enables direct observation of thermal photon bunching on sub-3.5 picosecond timescales without narrow spectral filtering, establishing pre-detection temporal imaging as a general platform for broadband statistical optics, with applications spanning ultrafast quantum optics, biophysical imaging, and potentially stellar intensity interferometry.

physics.optics↗

arXiv2026

Quantum interference between spectral bandwidth mismatched photons

Two-photon interference is a cornerstone of photonic quantum technologies. However, its practical use in hybrid architectures is constrained by the need for photon indistinguishability, particularly in linewidth and the associated time scale. While narrowband filtering can improve interference visibility, it introduces significant photon loss - a critical limitation for applications. Here, we experimentally demonstrate an efficient approach to enable non-classical two-photon interference between spectral-bandwidth mismatched photons using an electro-optic time lens. We increase the visibility of Hong-Ou-Mandel (HOM) interference between spectral bandwidth mismatched photons from $(31.0\pm1.7)\%$, to $(91.7\pm2.6)\%$, with correction for accidental coincidences, achieving highly non-classical two-photon interference visibility without spectral filtering. Moreover, we demonstrate a simultaneous correction of the central wavelength mismatch of $\pm1.1$ nm, while maintaining the non-classical interference visibility. This result opens the possibility to efficiently integrate quantum systems operating at different time scales for hybrid quantum communication, teleportation, entanglement swapping, distributed sensing, and hybrid quantum computing.

quant-ph↗

arXiv2026

High-Dimensional Quantum Photonics: Roadmap

The field of high-dimensional quantum photonics involves the use of multimode photonic degrees-of-freedom such as the spatial, temporal, or spectral structure of light to encode multi-level quantum states. Recent years have seen rapid progress in the development of methods to generate, manipulate, and distribute such quantum states of light and their use in a range of quantum technology applications that offer practical advantages over conventional qubit-based approaches. High-dimensional quantum states of light encoded in photonic time-bins, frequency-bins, transverse-spatial modes, waveguide paths, and temporal modes have enabled noise-robust fundamental tests of quantum mechanics, error-resilient and high-capacity quantum communication protocols, andas well as efficient approaches for quantum information processing, to name just a few examples. However, research in this field has progressed fairly independently, with little exchange across different photonic degrees-of-freedom or between experiment and theory and no comprehensive comparison between degrees-of-freedom. This roadmap aims to bridge this gap by surveying progress in each area and identifying shared challenges and opportunities that cut across two or more photonic degrees-of-freedoms. We review early work and state-of-the-art experimental techniques under development for high-dimensional quantum states encoded in single and entangled photons, as well as theoretical tools for their measurement and certification. We outline the main outstanding challenges for theory and each experimental degree-of-freedom, identifying promising future directions of research that may enable these to be overcome. We end by discussing interconnections and shared challenges centered around their distribution, measurement, and manipulation, with a view towards their integration into next-generation quantum technology platforms and applications.

quant-ph↗

arXiv2025

High-dimensional quantum key distribution with resource-efficient detection

While quantum key distribution (QKD) based on two-dimensional (qubit) encoding is a mature, field-tested technology, its performance is lacking for many cryptographic applications. High-dimensional encoding for QKD enables increased achievable key rates and robustness as compared to the standard qubit-based systems. However, experimental implementations of such systems are more complicated, expensive, and require careful security analysis as they are less common. In this work we present a proof of principle high-dimensional time-phase BB84 QKD experiment using only one single-photon detector per measurement basis. We employ the temporal Talbot effect to detect QKD symbols in the control basis, and show experimentally-obtained simplistic key rates for the two-dimensional and four-dimensional case, including in an urban fiber network. We present a comparison of a simplistic secret key rate obtained from a standard security proof with the one derived from a recently devised proof using a tunable beam splitter to display security issues stemming from asymmetric detection efficiencies in the two bases. Our results contribute to the discussion of the benefits of high-dimensional encoding and highlight the impact of security analysis on the achievable QKD performance.

quant-ph↗

arXiv2025

Quantum Key Distribution with Basis-Dependent Detection Probability

Quantum Key Distribution (QKD) is a promising technology for secure communication. Nevertheless, QKD is still treated with caution in certain contexts due to potential gaps between theoretical models and actual QKD implementations. A common assumption in security proofs is that the detection probability at the receiver, for a given input state, is independent of the measurement basis, which might not always be verified and could lead to security loopholes. This paper presents a security proof for QKD protocols that does not rely on the above assumption and is thus applicable in scenarios with detection probability mismatches, even when induced by the adversary. We demonstrate, through simulations, that our proof can extract positive key rates for setups vulnerable to large detection probability mismatches. This is achieved by monitoring whether an adversary is actively exploiting such vulnerabilities, instead of considering the worst-case scenario as in previous proofs. Our work highlights the importance of accounting for basis-dependent detection probabilities and provides a concrete solution for improving the security of practical QKD systems.

quant-ph↗

arXiv2025

Aberration-optimized electro-optic time lens with a tunable aperture

Time lenses have been recognized as crucial components for manipulating ultrafast optical pulses in various applications, from ultrafast spectroscopy to interfacing of optical quantum systems. However, the existing analytical model for the electro-optic time lens underutilizes its potential. Here, we introduce a tunable time aperture model for sinusoidal time lenses, enabling precise control over the chirp rate without modifying the device. We derive a closed-form expression for the maximum phase error and demonstrate its dependence on the time aperture. We experimentally validate the model by achieving a 1.6-fold enhanced spectral bandwidth compression of Gaussian pulses compared to the conventional approach. Our framework offers a practical tool for designing efficient temporal optical systems, benefiting applications such as temporal imaging and optical signal processing in both classical and quantum optics, where precise control over spectro-temporal properties is crucial.

physics.optics↗

arXiv2024

Interfacing picosecond and nanosecond quantum light pulses

Light is a key information carrier, enabling worldwide high-speed data transmission through a telecommunication fibre network. This information-carrying capacity can be extended to transmitting quantum information (QI) by encoding it in single photons -- flying qubits. However, various QI-processing platforms operate at vastly different timescales. QI-processing units in atomic media, operating within nanosecond to microsecond timescales, and high-speed quantum communication, at picosecond timescales, cannot be efficiently linked due to orders of magnitude mismatch in the timescales or, correspondingly, spectral linewidths. In this work, we develop a large-aperture time lens using complex high-bandwidth electro-optic phase modulation to bridge this gap. We demonstrate coherent, deterministic spectral bandwidth compression of quantum light pulses by more than two orders of magnitude with high efficiency. It will facilitate large-scale hybrid QI-processing by linking the ultrafast and quasi-continuous-wave experimental platforms, which until now, to a large extent, have been developing independently.

quant-ph↗

arXiv2023

Efficient detection of multidimensional single-photon time-bin superpositions

The ability to detect quantum superpositions lies at the heart of fundamental and applied aspects of quantum mechanics. The time-frequency degree of freedom of light enables encoding and transmitting quantum information in a multi-dimensional fashion compatible with fiber and integrated platforms. However, the ability to efficiently detect time-frequency superpositions is not yet available. Here we show, that multidimensional time-bin superpositions can be detected using a single time-resolved photon detector. Our approach uses off-the shelf components and is based on the temporal Talbot effect -- a time-frequency counterpart of the well-know near field diffraction effect. We provide experimental results and discuss the possible applications in quantum communication, quantum information processing, and time-frequency quantum state tomography.

physics.optics↗

arXiv2023

Reusing Comparator Networks in Pseudo-Boolean Encodings

A Pseudo-Boolean (PB) constraint is a linear inequality constraint over Boolean literals. One of the popular, efficient ideas used to solve PB-problems (a set of PB-constraints) is to translate them to SAT instances (encodings) via, for example, sorting networks, then to process those instances using state-of-the-art SAT-solvers. In this paper we show an improvement of such technique. By using a variation of a greedy set cover algorithm, when adding constraints to our encoding, we reuse parts of the already encoded PB-instance in order to decrease the size (the number of variables and clauses) of the resulting SAT instance. The experimental evaluation shows that the proposed method increases the number of solved instances.

cs.DS↗

arXiv2022

Electro-optic Fourier transform chronometry of pulsed quantum light

The power spectrum of an optical field can be acquired without a spectrally resolving detector by means of Fourier-transform spectrometry, based on measuring the temporal autocorrelation of the optical field. Analogously, we here perform temporal envelope measurements of ultrashort optical pulses without time resolved detection. We introduce the technique of Fourier transform chronometry, where the temporal envelope is acquired by measuring the frequency autocorrelation of the optical field in a linear interferometer. We apply our technique, which is the time-frequency conjugate measurement to Fourier-transform spectrometry, to experimentally measure the pulse envelope of classical and single photon light pulses.

physics.optics↗

arXiv2021

Linear-time algorithm for vertex 2-coloring without monochromatic triangles on planar graphs

In the problem of 2-coloring without monochromatic triangles (or triangle-tree 2-coloring), vertices of the simple, connected, undirected graph are colored with either 'black' or 'white' such that there are no 3 mutually adjacent vertices of the same color. In this paper we are positively answering the question posed in our previous work, namely, if there exists an algorithm solving 2-coloring without monochromatic triangles on planar graphs with linear-time complexity.

cs.DS↗

arXiv2020

Aperiodic electro-optic time lens for spectral manipulation of single-photon pulses

Electro-optic time lenses are promising experimental components for photonic spectral-temporal processing of quantum information. We report a stable method to realize an electro-optic time lens, which relies on the amplification of an electronic response of a fast photodiode. The method does not require a repetitive clock and may be applied to aperiodic optical signals. We experimentally demonstrate the approach using single-photon pulses and directly verify its aperiodicity. The approach will enable construction of complex electro-optic temporal optical systems.

physics.optics↗

arXiv2019

CNF Encodings of Cardinality Constraints Based on Comparator Networks

Boolean Satisfiability Problem (SAT) is one of the core problems in computer science. As one of the fundamental NP-complete problems, it can be used - by known reductions - to represent instances of variety of hard decision problems. Additionally, those representations can be passed to a program for finding satisfying assignments to Boolean formulas, for example, to a program called MiniSat. Those programs (called SAT-solvers) have been intensively developed for many years and - despite their worst-case exponential time complexity - are able to solve a multitude of hard practical instances. A drawback of this approach is that clauses are neither expressive, nor compact, and using them to describe decision problems can pose a big challenge on its own. We can improve this by using high-level constraints as a bridge between a problem at hand and SAT. Such constraints are then automatically translated to eqisatisfiable Boolean formulas. The main theme of this thesis revolves around one type of such constraints, namely Boolean Cardinality Constraints (or simply cardinality constraints). Cardinality constraints state that at most (at least, or exactly) k out of n propositional literals can be true. Such cardinality constraints appear naturally in formulations of different real-world problems including cumulative scheduling, timetabling or formal hardware verification. The goal of this thesis is to propose and analyze new and efficient methods to encode (translate) cardinality constraints into equisatisfiable proposition formulas in CNF, such that the resulting SAT instances are small and that the SAT-solver runtime is as short as possible.

cs.DS↗

arXiv2018

Entanglement Swapping for Generation of Heralded Time-Frequency-Entangled Photon Pairs

Photonic time-frequency entanglement is a promising resource for quantum information processing technologies. We investigate swapping of continuous-variable entanglement in the time-frequency degree of freedom using three-wave mixing in the low-gain regime with the aim of producing heralded biphoton states with high purity and low multi-pair probability. Heralding is achieved by combining one photon from each of two biphoton sources via sum-frequency generation to create a herald photon. We present a realistic model with pulsed pumps, investigate the effects of resolving the frequency of the herald photon, and find that frequency-resolving measurement of the herald photon is necessary to produce high-purity biphotons. We also find a trade-off between the rate of successful entanglement swapping and both the purity and quantified entanglement resource (negativity) of the heralded biphoton state.

quant-ph↗

arXiv2018

Experimental single-photon pulse characterization by electro-optic shearing interferometry

The ability to characterize the complete quantum state of light is essential for both fundamental and applied science. For single photons the quantum state is provided by the mode that it occupies. The spectral temporal mode structure of light has recently emerged as an essential means for quantum information science. Here we experimentally demonstrate a self-referencing technique to completely determine the pulse-mode structure of single photons by means of spectral shearing interferometry. We detail the calibration and resolution of the measurement and discuss challenges and critical requirements for future advances of this method.

physics.optics↗

arXiv2018

Measuring the single-photon temporal-spectral wave function

Temporal-spectral modes of light provide a fundamental window into the nature of atomic and molecular systems and offer robust means for information encoding. Methods to precisely characterize the temporal-spectral state of light at the single-photon level thus play a central role in understanding quantum emitters and are a key requirement for quantum technologies that harness single-photon states. Here we demonstrate an optical reference-free method, which melds techniques from ultrafast metrology and single-photon spectral detection, to characterize the temporal-spectral state of single photons. This provides a robust, wavelength-tunable approach for rapid characterization of pulsed single-photon states that underpins emerging optical quantum technologies based upon the temporal-spectral mode structure of quantum light.

quant-ph↗

arXiv2017

On vertex coloring without monochromatic triangles

We study a certain relaxation of the classic vertex coloring problem, namely, a coloring of vertices of undirected, simple graphs, such that there are no monochromatic triangles. We give the first classification of the problem in terms of classic and parametrized algorithms. Several computational complexity results are also presented, which improve on the previous results found in the literature. We propose the new structural parameter for undirected, simple graphs -- the triangle-free chromatic number $χ_3$. We bound $χ_3$ by other known structural parameters. We also present two classes of graphs with interesting coloring properties, that play pivotal role in proving useful observation about our problem. We give/ask several conjectures/questions throughout this paper to encourage new research in the area of graph coloring.

cs.DS↗

arXiv2017

Encoding Cardinality Constraints using Generalized Selection Networks

Boolean cardinality constraints state that at most (at least, or exactly) $k$ out of $n$ propositional literals can be true. We propose a new class of selection networks that can be used for an efficient encoding of them. Several comparator networks have been proposed recently for encoding cardinality constraints and experiments have proved their efficiency. Those were based mainly on the odd-even or pairwise comparator networks. We use similar ideas, but we extend the model of comparator networks so that the basic components are not only comparators (2-sorters) but more general $m$-sorters, for $m \geq 2$. The inputs are organized into $m$ columns, in which elements are recursively selected and, after that, columns are merged using an idea of multi-way merging. We present two algorithms parametrized by $m \geq 2$. We call those networks $m$-Wise Selection Network and $m$-Odd-Even Selection Network. We give detailed construction of the mergers when $m=4$. The construction can be directly applied to any values of $k$ and $n$. The proposed encoding of sorters is standard, therefore the arc-consistency is preserved. We prove correctness of the constructions and present the theoretical and experimental evaluation, which show that the new encodings are competitive to the other state-of-art encodings.

cs.DS↗