84 research outputs found
Mode structure of the radiation emitted through high-gain parametric down-conversion
No full textQuantumness and brightness of light are not usually found together in today’s optical quantum information, communication or measurement technologies. Yet, the last two decades saw an increased interest in the study of bright sources of nonclassical light where lossless control of their spatio-temporal spectrum promises to improve the capabilities of existing applications or to create novel ones. One of the most popular light sources for quantum optics is parametric down-conversion (PDC), a nonlinear process that occurs inside certain dielectrics where non-classical radiation originates from the parametric amplification of vacuum fluctuations. Even though
the PDC process is known for almost six decades, the quantum aspects of PDC have mostly been studied at low pump power regimes. In this case, much less than one photon per mode is spontaneously produced. At strong pump power regimes, where several photons per mode
are produced, PDC becomes a source of a multiphoton non-classical state of light known as bright squeezed vacuum (BSV). BSV is recognized as a good candidate for efficient light-light and light-matter interactions, multichannel quantum communications, parallel information
processing, high-resolution metrology and imaging, among other applications.
This thesis addresses one out of several unexplored questions regarding BSV, namely, what is its spatial modal structure? To answer this question, orthonormal modes dictated by the spatial
coherence of the radiation (or so-called Schmidt modes) which also account for photon number
correlations, have been considered. The Schmidt-mode formalism has been successfully used in
the description of the radiation generated by low-gain PDC but their usage in the BSV case was challenging. This thesis presents several experiments that validated the results of an analytical
theory for BSV based on Schmidt modes. According to the theory, the modes describing BSV, to a good approximation, are invariant to the pump power used in the process, while the photon
population of each mode is not. The observed changes in the spatial intensity spectrum, spatial photon number correlations and the effects of the spatial anisotropy on the spectrum shape corroborated this prediction.
Additionally, different methods for engineering the spatial spectrum of BSV were proposed and implemented by using unseeded and strongly pumped traveling-wave optical parametric amplifiers (OPAs) made of bulk nonlinear crystals, where the radiation produced is highly multimode in several degrees of freedom. For instance, spatial walk-off was exploited to obtain
tunable, bright, narrowband and diffraction-limited twin beams through the amplification of the
radiation in the direction of the pump Poynting vector. Alternatively, tailoring of the BSV state was achieved through the amplification of the radiation produced in one unseeded traveling-wave
OPA by the presence of a second OPA, up to the generation of a single spatial mode. The modal content of the output light was further studied in terms of radial and orbital angular momentum
modes. Finally, as an alternative to generation, lossless projective filtering of a single spatial BSV mode by means of a single-mode fiber was performed. The examples given in this thesis
on the lossless control of the BSV spatial spectrum are extensible to the temporal domain, as proved in subsequent works. Since the elucidation of the mode structure of BSV radiation is
a requirement for further development of reliable light tailoring strategies that preserve BSV nonclassical properties, this thesis is a direct contribution to the know-how that will allow full
involvement of BSV in quantum technologies in the near future
Nonlinear interferometry with high-gain parametric down-conversion
No full textInterferometers have become essential devices within research and industry because they can measure phase shifts, often very small ones. Increasing the number of probing photons enhances the accuracy of this measurement, but with a bounded scaling called the shot-noise limit. The field of nonlinear interferometry studies how to surpass this limit using nonclassical properties produced with nonlinear effects. The advantage offered -- often referred to as super-sensitivity -- becomes relevant when the precision cannot be pushed further, for instance, by an arbitrary increase of the number of photons. Therefore, this field pioneers the technological advance of interferometers and, in the last decades, it had a substantial impact on applications in quantum information, metrology and imaging.
This thesis aims to demonstrate robust and versatile nonlinear interferometers that encompass the process of parametric down-conversion in nonlinear crystals as the source of nonclassical radiation. The squeezed vacuum state produced in this process can yield a macroscopic number of photons per mode in the strongly-pumped regime while still possessing quantum features. This state is injected together with a laser in a classical interferometer for the first experiment of this work. The super-sensitivity to a scalar phase shift results from the reduced noise in one electric field quadrature, a nonclassical feature. However, the output state can be fragile if the detection is lossy or inefficient; this work proves that noiseless optical amplification before detection leads to robustness and that a stronger amplification pre-compensates for a higher loss or inefficiency. This proof-of-principle scheme is suitable for many applications employing squeezed states, especially in those challenging wavelength ranges for detection like mid-infrared.
The noiseless amplification is obtained here with the external stimulation of the down-conversion process in similar nonlinear crystals to the ones used to produce the squeezed vacuum. The measurement of a scalar phase shift does not fully exploit the potential of the squeezed vacuum and the amplification process: the broad multimode spatial structure would enable two-dimensional phase super-sensitivity. However, since the amplification in nonlinear crystals is not necessarily noiseless, as a preliminary step, this thesis addresses the unexplored conditions on the input signal to achieve this regime for the spatially-multimode case. The examples given here for the spatial degree are extensible also to the temporal domain, which is of great interest for quantum spectroscopy.
This thesis proposes another scheme, usually referred to as the SU(1,1) interferometer, to pave the way towards two-dimensional super-sensitivity. In this scheme, the beam splitter, which is a passive building block of interferometers, is substituted with the nonlinear crystal, a pumped active element, and no other source than the squeezed vacuum may be required. Previous experiments achieved super-sensitive detection of scalar phase shifts, but the novel configuration presented here works with multiple spatial modes and in two dimensions. The operation in the quantum regime is ensured by the measured reduction in the quadrature noise for the plane-wave modes of the state that probes the phase shift. As the phase changes, this configuration is also stable in the output spatial mode content, both in the radial and azimuthal degree of freedom. The full mode structure for this interferometer is not analytically known; this thesis proposes a method to experimentally reconstruct the modes with the acquisition of only intensity distributions. The knowledge of this structure is fundamental for applications in remote sensing and sub-shot-noise imaging because it helps developing schemes that preserve the nonclassical properties, nontrivial for multiple modes
Elementy naturalizma i simvolizma v proizvedenii︠a︡kh Chekhova, 1888-1897
No full textThis thesis was scanned from the print manuscript for digital preservation and is copyright the author.
Researchers can access this thesis by asking their local university, institution or public library to
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Wigner Function Tomography via Optical Parametric Amplification
No full textWigner function tomography is indispensable for characterizing quantum
states, but its commonly used version, balanced homodyne detection, suffers
from several weaknesses. First, it requires efficient detection, which is
critical for measuring fragile non-Gaussian states, especially bright ones.
Second, it needs a local oscillator, tailored to match the spatiotemporal
properties of the state under test, and fails for multimode and broadband
states. Here we propose Wigner function tomography based on optical parametric
amplification followed by direct detection. The method is immune to detection
inefficiency and loss, and suitable for broadband, spatially and temporally
multimode quantum states. To prove the principle, we experimentally reconstruct
the Wigner function of squeezed vacuum occupying a single mode of a strongly
multimode state. We obtain a squeezing of dB and a purity of
despite more than loss caused mainly by
filtering. Theoretically, we also consider the reconstruction of a squeezed
single photon - a bright non-Gaussian state. Due to strong multimode parametric
amplification, the method allows for the simultaneous tomography of multiple
modes. This makes it a powerful tool for optical quantum information
processing
Time-resolved purification of photon pairs from ultrasmall sources
No full textGeneration of entangled photons through spontaneous parametric
down-conversion (SPDC) from ultrasmall sources like thin films, metasurfaces,
or nanoantennas, offers unprecedented freedom in quantum state engineering.
However, as the source of SPDC gets smaller, the role of photoluminescence
increases, which leads to the contamination of two-photon states with thermal
background. Here we propose and implement a solution to this problem: by using
pulsed SPDC and time distillation, we increase the purity and the heralding
efficiency of the photon pairs. In the experiment, we increase the purity of
two-photon states generated in a 7 m film of lithium niobate from 0.002 to
0.99. With the higher purity, we were able to observe and characterize
different polarization states of photon pairs generated simultaneously due to
relaxed phase matching. In particular, we showed the presence of orthogonally
polarized photons, potentially usable for the generation of polarization
entanglement
Bright squeezed vacuum for two-photon spectroscopy: simultaneously high resolution in time and frequency, space and wavevector
No full textEntangled photons offer two advantages for two-photon absorption spectroscopy. One of them, the linear scaling of two-photon absorption rate with the input photon flux, is only valid at very low photon fluxes and is therefore impractical. The other is the overcoming of the classical constraints for simultaneous resolution in time-frequency and in space-wavevector. Here we consider bright squeezed vacuum (BSV) as an alternative to entangled photons. The efficiency increase it offers in comparison with coherent light is modest, but it does not depend on the photon flux. Moreover, and this is what we show in this work, BSV also provides simultaneously high resolution in time and frequency, and in space and wavevector. In our experiment, we measure the widths of the second-order correlation functions in space, time, frequency, and angle, and demonstrate the violation of the constraint given by the Fourier transformation, also known as the Mancini criterion of entanglement
"...Incognito the damned!"(A. P. Chekhov's stories "Two in one" and Teffi "Incognito"). Lesson-comparison in 11th grade
No full textThe article presents the draft of lessons for the11th grade for the study of Taffy's works. The author points to the effectiveness of a comparative approach and offers his own version of comparing the texts by Gogol ("Inspector"), Chekhov ("Two in One") and Taffy ("Incognito"). In the present studies the author analyzes the terms of the basic features of comic art of Taffy, allusive backdrop of her story "Incognito." The author considers in detail how the theme of a little man is refracted in these three works, how the heroes of the situation are disclosed in the "incognito"
Chehov's Aphorisms in Space of a Valuable Choice of Pupils
No full textThe author offers the methodology of conducting lessons of speech development by A.P.Chekhov's aphorisms, due to that pupils include in active dialogue with the writer and this methodology brings up to date readers-schoolboys valuable self-determination
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