arXiv subjects

Radosław Chrapkiewicz

Publications and source records attributed to Radosław Chrapkiewicz.

9 recordsLinked to original sources

arXiv2023

Noise Resistant Phase Imaging with Intensity Correlation

Interferometric methods, renowned for their reliability and precision, play a vital role in phase imaging. Interferometry typically requires high coherence and stability between the measured and the reference beam. The presence of rapid phase fluctuations averages out the interferogram, erasing the spatial phase information. This difficulty can be circumvented by shortening the measurement time. However, shortening the measurement time results in smaller photon counting rates precluding its applicability to low-intensity phase imaging. We introduce and experimentally demonstrate a phase imaging technique that is immune to position-independent, time-dependent phase fluctuation. We accomplish this by measuring intensity correlation instead of intensity. Our method enables using long measurement times and is therefore advantageous when the photon flux is very low. We use a Fisher information-based approach to show that the precision of phase reconstruction achieved using our method is in fact the best achievable precision in the scenario when two photons are detected per phase stability time.

physics.optics↗

arXiv2017

High-Capacity Angularly-Multiplexed Holographic Memory Operating at the Single Photon Level

We experimentally demonstrate an angularly-multiplexed holographic memory capable of intrinsic generation, storage and retrieval of multiple photons, based on off-resonant Raman interaction in warm rubidium-87 vapors. The memory capacity of up to 60 independent atomic spin-wave modes is evidenced by analyzing angular distributions of coincidences between Stokes and time-delayed anti-Stokes light, observed down to the level of single spin-wave excitation during several-$μ$s memory lifetime. We also propose how to practically enhance rates of single and multiple photons generation by combining our multimode emissive memory with existing fast optical switches.

quant-ph↗

arXiv2016

Mode engineering for realistic quantum-enhanced interferometry

Quantum metrology overcomes standard precision limits by exploiting collective quantum superpositions of physical systems used for sensing, with the prominent example of non-classical multiphoton states improving interferometric techniques. Practical quantum-enhanced interferometry is, however, vulnerable to imperfections such as partial distinguishability of interfering photons. Here we introduce a method where appropriate design of the modal structure of input photons can alleviate deleterious effects caused by another, experimentally inaccessible degree of freedom. This result is accompanied by a laboratory demonstration that a suitable choice of spatial modes combined with position-resolved coincidence detection restores entanglement-enhanced precision in the full operating range of a realistic two-photon Mach-Zehnder interferometer, specifically around a point which otherwise does not even attain the shot-noise limit due to the presence of residual distinguishing information in the spectral degree of freedom. Our method highlights the potential of engineering multimode physical systems in metrologic applications.

quant-ph↗

arXiv2016

Hologram of a Single Photon

The spatial structure of single photons is becoming an extensively explored resource used for facilitating the free-space quantum key distribution and quantum computation as well as for benchmarking the limits of quantum entanglement generation with orbital angular momentum modes or reduction of the photon free-space propagation speed. Albeit nowadays an accurate tailoring of photon's spatial structure is routinely performed using methods employed for shaping classical optical beams, the reciprocal problem of retrieving the spatial phase-amplitude structure of an unknown single photon cannot be solved using complimentary classical holography techniques exhibiting excellent interferometric precision. Here we introduce a method to record a hologram of a single photon (HSP) probed by another reference photon, based on essentially different concept of quantum interference between two-photon probability amplitudes. Similarly to classical holograms, HSP encodes full information about photon's "shape", i.e. its quantum wavefunction whose local amplitude and phase are retrieved in the demonstrated experiment.

quant-ph↗

arXiv2015

Magnetically tuned, robust and efficient filtering system for spatially multimode quantum memory in warm atomic vapors

Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here we report a combination of magnetically tuned absorption and Faraday filters, both light-direction-insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal to noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman-scattered photons.

quant-ph↗

arXiv2015

Photon counts statistics of squeezed and multi-mode thermal states of light on multiplexed on-off detectors

Photon number resolving detectors can be highly useful for studying the statistics of multi-photon quantum states of light. In this work we study the counts statistics of different states of light measured on multiplexed on-off detectors. We put special emphasis on artificial nonclassical features of the statistics obtained. We show new ways to derive analytical formulas for counts statistics and their moments. Using our approach we are the first to derive statistics moments for multi-mode thermal states measured on multiplexed on-off detectors. We use them to determine empirical Mandel parameters and recently proposed subbinomial parameters suitable for tests of nonclassicality of the measured states. Additionally, we investigate subpoissonian and superbunching properties of the two-mode squeezed state measured on a pair of multiplexed detectors and we present results of the Fano factor and second-order correlation function for these states.

quant-ph↗

arXiv2015

Shot-by-shot imaging of Hong-Ou-Mandel interference with an intensified sCMOS camera

We report the first observation of Hong-Ou-Mandel (HOM) interference of highly indistinguishable photon pairs with spatial resolution. Direct imaging of two-photon coalescence with an intensified sCMOS camera system clearly reveals spatially separated photons appearing pairwise within one of the two modes. With the use of the camera system we quantified the number of pairs and recovered the full HOM dip yielding 96.3% interference visibility, as well as retrieved the number of coalesced pairs. We retrieved the spatial mode structure of both interfering photons by performing a proof-of-principle demonstration of a new, low noise high resolution coincidence imaging scheme.

quant-ph↗

arXiv2014

Hamiltonian design in readout from room-temperature Raman atomic memory

We present an experimental demonstration of the Hamiltonian manipulation in light-atom interface in Raman-type warm rubidium-87 vapor atomic memory. By adjusting the detuning of the driving beam we varied the relative contributions of the Stokes and anti-Stokes scattering to the process of four-wave mixing which reads out a spatially multimode state of atomic memory. We measured the temporal evolution of the readout fields and the spatial intensity correlations between write-in and readout as a function of detuning with the use of an intensified camera. The correlation maps enabled us to resolve between the anti-Stokes and the Stokes scattering and to quantify their contributions. Our experimental results agree quantitatively with a simple, plane-wave theoretical model we provide. They allow for a simple interpretation of the coaction of the anti-Stokes and the Stokes scattering at the readout stage. The Stokes contribution yields additional, adjustable gain at the readout stage, albeit with inevitable extra noise. Here we provide a simple and useful framework to trace it, which is significant to the existing atomic memories setups. Furthermore, the shown Hamiltonian manipulation offers a broad range of atom-light interfaces readily applicable in current and future quantum protocols with atomic ensembles.

quant-ph↗

arXiv2014

Spontaneous and parametric processes in warm rubidium vapours

Warm rubidium vapours are known to be a versatile medium for a variety of experiments in atomic physics and quantum optics. Here we present experimental results on producing the frequency converted light for quantum applications based on spontaneous and stimulated processes in rubidium vapours. In particular, we study the efficiency of spontaneously initiated stimulated Raman scattering in the Λ-level configuration and conditions of generating the coherent blue light assisted by multi-photon transitions in the diamond-level configuration. Our results will be helpful in search for new types of interfaces between light and atomic quantum memories.

physics.atom-ph↗