Radosław Chrapkiewicz

Stanford University | SU

The power of optical holography stems from its ability to reveal complete, phase-amplitude spatial information about detected light. Standard holographic methods require a well-defined phase relation between measured and reference beams that is fundamentally impossible to fulfill for a single photon due to its entirely indeterminate global phase. W...

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 distinguis...

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 quant...

We apply collective Raman scattering to create, store and retrieve spatially multimode light in warm rubidium-87 vapors. The light is created in a spontaneous Stokes scattering process. This is accompanied by the creation of counterpart collective excitations in the atomic ensemble - the spin waves. After a certain storage time we coherently conver...

We experimentally demonstrate an angularly-multiplexed holographic memory capable of intrinsic generation, storage and retrieval of 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 St...

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...

Genetically encoded fluorescent voltage indicators are ideally suited to reveal the millisecond-scale interactions among and between targeted cell populations. However, current indicators lack the requisite sensitivity for in vivo multipopulation imaging. We describe next-generation green and red voltage sensors, Ace-mNeon2 and VARNAM2, and their r...

Brain circuits are composed of vast numbers of intricately interconnected neurons with diverse molecular, anatomical and physiological properties. To allow highly specific “user-defined” targeting of individual neurons for structural and functional studies, we modified three site-specific DNA recombinases, Cre, Dre and Flp, by combining them with a...

How the brain processes information accurately despite stochastic neural activity is a longstanding question¹. For instance, perception is fundamentally limited by the information that the brain can extract from the noisy dynamics of sensory neurons. Seminal experiments2,3 suggest that correlated noise in sensory cortical neural ensembles is what l...

Two-photon microscopy is a mainstay technique for imaging in scattering media and normally provides frame-acquisition rates of ~10–30 Hz. To track high-speed phenomena, we created a two-photon microscope with 400 illumination beams that collectively sample 95,000–211,000 µm² areas at rates up to 1 kHz. Using this microscope, we visualized microcirc...

We experimentally demonstrate a phase imaging technique which is resistant to time dependent phase fluctuations based on measuring intensity correlations instead of intensities. The method allows for long measurements, advantageous under low photon fluxes.

We experimentally demonstrate an angularly multiplexed holographic memory capable of intrinsic generation, storage, and retrieval of multiple photons, based on an 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 coincidenc...

We experimentally show that the complex transversal wavefunction of the unknown photon can be fully recovered from the spatially-resolved coincidence pattern resulting from its two-photon interference with the reference photon.

Raman scattering emissive multimode quantum memory setup is presented. The memory enables storage of photonic position-momentum entanglement, demonstrating a time-delayed Einstein-Podolsky-Rosen paradox.

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...

arXiv:1507.08963 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-ins...

We report first experimental demonstration of a warm atomic memory operating at a single-photon-level, capable to store and retrieve up to 120 spatial modes. We present unambiguous spatial g(2)(ΘS,ΘAS) cross-correlations between heralding and retrieved photons stored up to several microseconds.

Practical realizations of quantum-enhanced interferometry are vulnerable to imperfections such as the residual spectral distinguishability of interfering photons. We demonstrate experimentally that a careful design of the spatial structure of used photons, combined with position-resolved coincidence detection at the output, allows one to recover qu...

We demonstrate experimentally that a careful design of the spatial structure of interfered photons, combined with position-resolved coincidence detection, allows to recover sub-shot-noise phase sensitivity in regime that otherwise cannot even attain the shot-noise limit.

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 spontaneousl...

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 stat...

Photon number resolving detectors can be highly useful for studying the statistics of multiphoton 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 deri...

We present a method for spatially resolved multiphoton counting based on an intensified camera with the retrieval of multimode photon statistics fully accounting for non-linearities in the detection process. The scheme relies on one-time quantum tomographic calibration of the detector. Faithful, high-fidelity reconstruction of single- and two-mode...

We show that quantum memories can be implemented in atomic ensembles in a multi-spatial-mode regime using collective Raman scattering. It can be accomplished by optimization of diffusional decoherence which we measure by a novel method. OCIS codes: (290.5860) Scattering, Raman; (030.4070) Modes; (020.0020) Atomic and molecular physics.

Here we present results of measuring spatially multimode collective Raman scattering in warm Rubidium vapors. It is the first to our knowledge generation, storing and retrieval of spatially multimode light in such process. We also suggest a new, direct method of measuring diffusion coefficients by measuring decoherence of collective excitations in...

We found the full information of the output multimode state in the Spontaneous Parametric Down-Conversion, in the lossy 1D waveguide, still manifesting quantum behavior. We refer the results to the Raman scattering in atomic media.

Przeprowadziłem szereg eksploracyjnych badań zjawiska wzmocnienia i rozpraszania Ramana w parach Rb87. Dzięki uzyskanym wynikom i wnioskom zbudowałem układ, w którym za- obserwowałem efekt pamięci kwantowej z czasem przechowywania do 17µs. W procesie sto- kesowskiego i opóźnionego w czasie antystokesowskiego rozproszenia Ramana wytworzyłem dwumodow...

We study the process of multimode Spontaneous Parametric Down--Conversion (SPDC) in the lossy, one dimensional waveguide. We propose a description using first order Correlation Functions (CF) in the fluorescence fields, as a very fruitful and easy approach providing us with a complete information about the final multimode state. We formulate the eq...