Nonclassical Light Research Articles

XX International Youth Scientific School “Coherent Optics and Optical Spectroscopy”

The XX International Youth School on Coherent Optics and Optical Spectroscopy (COOS2016) was held in Kazan, Russia, from October 18 to October 20 on the Nikolai Lobachevsky Scientific Library of Kazan Federal University. The School follows the global tendency to comprehensive studies of matter properties and its interaction with electromagnetic fields. Since 1997 more than 100 famous scientists from USA, Germany, Ukraine, Belarus and Russia had plenary lectures presentations. This is the right place, where over 1000 young scientists had an opportunity to participate in hot discussions of the latest scientific news. Many young people have submitted interesting reports on photonics, quantum electronics, laser physics, quantum optics, traditional optical and laser spectroscopy, non-linear optics, material science and nanotechnology. Here we are publishing the full-size papers prepared from the most interesting lectures and reports selected by the Program Committee of the School. Plenary sessions were offered by the following invited speakers:Ildar Gabitov, University of Arizona, USA.• Error statistics in coherent communication linesAndrei Naumov, Institute for Spectroscopy RAS, Troitsk, Moscow, Russia.• Revisiting the question of the experimental realization of a nonclassical light source on the basis of single organic molecules of dyesGerd Hermann, University of Giessien, Germany.• Applications of Coherent SpectroscopyAskhat Basharov, National Research Center ‘Kurchatov Institute’, Moscow, Russia.• Low-frequency emission in resonant processes• Evolution of a two-level quantum particle in the noise classical e.-m. field within and beyond the resonant approximationAnastas Bukharaev, Kazan E. K. Zavoisky Physical-Technical Institute, Kazan, Russia.• StraintronicsMaxim Gladush, Institute for Spectroscopy RAS, Troitsk, Moscow, Russia.• Fluorescent properties of single quantum emitters and their ensembles in dielectric mediaSergey Sazonov, National Research Center “Kurchatov Institute”, Moscow, Russia.• On the approximations of slowly varying envelope and slowly varying profile in nonlinear optics equationsAlexey Kalachev, Kazan E. K. Zavoisky Physical-Technical Institute, Kazan, Russia.• Quantum memory in an isotopically pure crystalsRenat Gainutdinov, Kazan Federal University, Kazan, Russia.• Atomic hydrogen spectroscopy and problems of modern physics applicationsVladimir Dresvyanskiy, Irkutsk branch of the Institute of Laser Physics SB RAS, Irkutsk, Russia.• Photophysical processes in single radiation defects and their ensemblesIlfan Bikmaev, Kazan Federal University, Kazan, Russia.• Optical spectroscopy in astrophysicsPROGRAM COMMITTEEGabitov Ildar Ravilievich – co-chairmanDr. Sc. (Phys.-Math.), Professor at University of Arizona, USANaumov Andrey Vitalievich - co-chairmanDr. Sc. (Phys.-Math.), Professor, deputy director at Institute for Spectroscopy RAS Salakhov Myakzyum KhalimullovichDr. Sc. (Phys.-Math.), academician of the Tatarstan Academy of Sciences, president the Tatarstan Academy of Sciences Samartsev Vitalii VladimirovichDr. Sc. (Phys.-Math.), academician of the Russian Academy of Natural Science, Professor at Kazan E. K. Zavoisky Physical-Technical Institute (KPhTI)Gainutdinov Renat KhamitovichDr. Sc. (Phys.-Math.), professor at Kazan Federal UniversityORGANIZING COMMITTEESalakhov Myakzyum Khalimullovich – rector of the SchoolSamartsev Vitalii Vladimirovich – vice-rector of the SchoolKamalova Dina Ilevna – scientific secretary of the SchoolThis proceedings volume contains papers reported at the conference. The Proceedings of the XX International Youth School on Coherent Optics and Optical Spectroscopy (COOS2016) were edited by Salakhov Myakzyum Khalimullovich, Samartsev Vitalii Vladimirovich and Gainutdinov Renat Khamitovich with the assistance of Petrova Alexandra Sergeevna as copy editor.We are grateful to Russian Foundation for Basic Research, Tatarstan Academy of Science, Kazan E.K. Zavoisky Physical-Technical Institute for financial.Salakhov Myakzyum Khalimullovich, EditorSamartsev Vitalii Vladimirovich, EditorGainutdinov Renat Khamitovich, Editor

Probing free-space quantum channels with laboratory-based experiments

Atmospheric channels are a promising candidate to establish secure quantum communication on a global scale. However, due to their turbulent nature, it is crucial to understand the impact of the atmosphere on the quantum properties of light and examine it experimentally. In this paper, we introduce a method to probe atmospheric free-space links with quantum light on a laboratory scale. In contrast to previous works, our method models arbitrary intensity losses caused by turbulence to emulate general atmospheric conditions. This allows us to characterize turbulent quantum channels in a well-controlled manner. To implement this technique, we perform a series of measurements with different constant attenuations and simulate the fluctuating losses by combining the obtained data. We directly test the proposed method with an on-chip source of nonclassical light and a time-bin-multiplexed detection system. With the obtained data, we characterize the nonclassicality of the generated states for different atmospheric noise models and analyze a post-selection protocol. This general technique in atmospheric quantum optics allows for studying turbulent quantum channels and predicting their properties for future applications.

Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

The development of scalable sources of non-classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near-optimal sources of indistinguishable single photons. However, their performance as sources of entangled-photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski–Krastanov InGaAs quantum dots have shown non-optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguishability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dot entanglement sources in future quantum technologies.

Coherent control of atomic qubits by non-classical light

In this work we investigate analytically the interaction between a quantum atomic model system and non-classical light and suggest a method to transfer phase information from the field qubit to the atomic one. A rather realistic atomic system with bound levels and the continuum is considered. The influence of ionization on the possibility of the phase transfer is analyzed. The atomic state formed during the interaction is shown to be controlled by the relative phase of the field qubit. The possibility to measure the transferred phase is demonstrated.

Proposal for witnessing non-classical light with the human eye

We give a complete proposal showing how to detect the non-classical nature of photonic states with naked eyes as detectors. The enabling technology is a sub-Poissonian photonic state that is obtained from single photons, displacement operations in phase space and basic non-photon-number-resolving detectors. We present a detailed statistical analysis of our proposal including imperfect photon creation and detection and a realistic model of the human eye. We conclude that a few tens of hours are sufficient to certify non-classical light with the human eye with a p-value of 10%.

Detector-Independent Verification of Quantum Light.

We introduce a method for the verification of nonclassical light which is independent of the complex interaction between the generated light and the material of the detectors. This is accomplished by means of a multiplexing arrangement. Its theoretical description yields that the coincidence statistics of this measurement layout is a mixture of multinomial distributions for any classical light field and any type of detector. This allows us to formulate bounds on the statistical properties of classical states. We apply our directly accessible method to heralded multiphoton states which are detected with a single multiplexing step only and two detectors, which are in our work superconducting transition-edge sensors. The nonclassicality of the generated light is verified and characterized through the violation of the classical bounds without the need for characterizing the used detectors.

(Invited) Waveguide Integrated Electrically Driven Carbon Nanotube Light Sources

I will report on our recent success in fabricating waveguide-integrated carbon nanotube light sources with superconducting single photon detectors. This complete quantum photonic circuit allows for on-chip correlation experiments to explore non-classical light emission. I will furthermore explain how the photonic environment can be used to tailor the emission wavelength and linewidth of a nanotube emitter and the feasibility of carbon nanotube transducers for fast signal processing. [1] F. Pyatkov et al., Nature Photonics 10 (2016), pp. 420.[2] S. Khasminskaya et al., Nature Photonics 10 (2016), pp. 727. Figure 1

On-Chip Architecture for Self-Homodyned Nonclassical Light

In the last decade, there has been remarkable progress on the practical integration of on-chip quantum photonic devices yet quantum state generators remain an outstanding challenge. Simultaneously, the quantum-dot photonic-crystal-resonator platform has demonstrated a versatility for creating nonclassical light with tunable quantum statistics, thanks to a newly discovered self-homodyning interferometric effect that preferentially selects the quantum light over the classical light when using an optimally tuned Fano resonance. In this work, we propose a general structure for the cavity quantum electrodynamical generation of quantum states from a waveguide-integrated version of the quantum-dot photonic-crystal-resonator platform, which is specifically tailored for preferential quantum state transmission. We support our results with rigorous Finite-Difference Time-Domain and quantum optical simulations, and show how our proposed device can serve as a robust generator of highly pure single- and even multi-photon states.

A bright triggered twin-photon source in the solid state

A non-classical light source emitting pairs of identical photons represents a versatile resource of interdisciplinary importance with applications in quantum optics and quantum biology. To date, photon twins have mostly been generated using parametric downconversion sources, relying on Poissonian number distributions, or atoms, exhibiting low emission rates. Here we propose and experimentally demonstrate the efficient, triggered generation of photon twins using the energy-degenerate biexciton–exciton radiative cascade of a single semiconductor quantum dot. Deterministically integrated within a microlens, this nanostructure emits highly correlated photon pairs, degenerate in energy and polarization, at a rate of up to (234±4) kHz. Furthermore, we verify a significant degree of photon indistinguishability and directly observe twin-photon emission by employing photon-number-resolving detectors, which enables the reconstruction of the emitted photon number distribution. Our work represents an important step towards the realization of efficient sources of twin-photon states on a fully scalable technology platform.

Electrically-Pumped Wavelength-Tunable GaAs Quantum Dots Interfaced with Rubidium Atoms.

We demonstrate the first wavelength-tunable electrically pumped source of nonclassical light that can emit photons with wavelength in resonance with the D2 transitions of 87Rb atoms. The device is fabricated by integrating a novel GaAs single-quantum-dot light-emitting diode (LED) onto a piezoelectric actuator. By feeding the emitted photons into a 75 mm long cell containing warm 87Rb vapor, we observe slow-light with a temporal delay of up to 3.4 ns. In view of the possibility of using 87Rb atomic vapors as quantum memories, this work makes an important step toward the realization of hybrid-quantum systems for future quantum networks.

Emission properties of single-photon sources based on CdTe/ZnTe quantum dots

We report on single photon emission from single CdTe/ZnTe quantum dots (QDs) grown by thermally-activated molecular beam epitaxy providing a reduced QD lateral density below 1010 cm-2. For micro-photoluminescence spectroscopy studies and correlation measurements, the mesa structures of 200 and 500 nm diameters are fabricated by combination of electron-beam lithography and reactive plasma etching. Autocorrelation function of photons emitted from a single QD under cw excitation demonstrates antibunching with a value of g(2)(0) ∼ 0.3 that is a signature of non-classical light.

Spectral Shearing of Quantum Light Pulses by Electro-Optic Phase Modulation.

Frequency conversion of nonclassical light enables robust encoding of quantum information based upon spectral multiplexing that is particularly well-suited to integrated-optics platforms. Here we present an intrinsically deterministic linear-optics approach to spectral shearing of quantum light pulses and show it preserves the wave-packet coherence and quantum nature of light. The technique is based upon an electro-optic Doppler shift to implement frequency shear of heralded single-photon wave packets by ±200 GHz, which can be scaled to an arbitrary shift. These results demonstrate a reconfigurable method to controlling the spectral-temporal mode structure of quantum light that could achieve unitary operation.

Subcycle quantum electrodynamics.

Squeezed states of electromagnetic radiation have quantum fluctuations below those of the vacuum field. They offer a unique resource for quantum information systems and precision metrology, including gravitational wave detectors, which require unprecedented sensitivity. Since the first experiments on this non-classical form of light, quantum analysis has been based on homodyning techniques and photon correlation measurements. These methods currently function in the visible to near-infrared and microwave spectral ranges. They require a well-defined carrier frequency, and photons contained in a quantum state need to be absorbed or amplified. Quantum non-demolition experiments may be performed to avoid the influence of a measurement in one quadrature, but this procedure comes at the expense of increased uncertainty in another quadrature. Here we generate mid-infrared time-locked patterns of squeezed vacuum noise. After propagation through free space, the quantum fluctuations of the electric field are studied in the time domain using electro-optic sampling with few-femtosecond laser pulses. We directly compare the local noise amplitude to that of bare (that is, unperturbed) vacuum. Our nonlinear approach operates off resonance and, unlike homodyning or photon correlation techniques, without absorption or amplification of the field that is investigated. We find subcycle intervals with noise levels that are substantially less than the amplitude of the vacuum field. As a consequence, there are enhanced fluctuations in adjacent time intervals, owing to Heisenberg's uncertainty principle, which indicate generation of highly correlated quantum radiation. Together with efforts in the far infrared, this work enables the study of elementary quantum dynamics of light and matter in an energy range at the boundary between vacuum and thermal background conditions.

Second-order temporal interference of two independent light beams at an asymmetrical beam splitter**Project supported by the National Natural Science Foundation of China (Grant No. 11404255), the Doctor Foundation of Education Ministry of China (Grant No. 20130201120013), the Programme of Introducing Talents of Discipline to Universities, China (Grant No. B14040), and the Fundamental Research Funds for the Central Universities, China.

The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman’s path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.

Generation of Nonclassical Light by Unsaturated Two-Photon Absorption

In this paper, we investigate the distribution statistics of photons in a single mode radiation field subjected to two-photon absorption (TPA) and the factors that contribute to squeezing and antibunching of photons, leading to the generation of nonclassical light. TPA is a nonlinear optical phenomenon in which the atoms interact with the light field by absorbing two photons simultaneously. The motivation to study TPA is the recent intense activity on nanocrystallites/quantum dots. Further, it is the only nonlinear optical phenomenon that can be analytically studied. The simultaneous occurrence of squeezing and antibunching is studied with small initial photon numbers by solving the master equation for TPA of a single mode radiation directly by numerical integration, without going through analytical procedure. The results are compared with those of analytical/numerical procedures available. Further, the discussion on the parameters of squeezing and antibunching for short-time (ST) as well as long-time is done comprehensively in the present work by taking up the ST approximation and summation of ST (SST) procedure along with the exact numerical method.

A high repetition rate experimental setup for quantum non-linear optics with cold Rydberg atoms

Using electromagnetically induced transparency and photon storage, the strong dipolar interactions between Rydberg atoms and the resulting dipole blockade can be mapped onto light fields to realise optical non-linearities and interactions at the single photon level. We report on the realisation of an experimental apparatus designed to study interactions between single photons stored as Rydberg excitations in optically trapped microscopic ensembles of ultracold 87Rb atoms. A pair of in-vacuum high numerical aperture lenses focus excitation and trapping beams down to 1 μm, well below the Rydberg blockade. Thanks to efficient magneto-optical trap (MOT) loading from an atomic beam generated by a 2D MOT and the ability to recycle the microscopic ensembles more than 20000 times without significant atom loss, we achieve effective repetition rates exceeding 110 kHz to obtain good photon counting statistics on reasonable time scales. To demonstrate the functionality of the setup, we present evidence of strong photon interactions including saturation of photon storage and the retrieval of non-classical light. Using in-vacuum antennae operating at up to 40 GHz, we perform microwave spectroscopy on photons stored as Rydberg excitations and observe an interaction induced change in lineshape depending on the number of stored photons.

Quantum enhanced feedback cooling of a mechanical oscillator using nonclassical light.

Laser cooling is a fundamental technique used in primary atomic frequency standards, quantum computers, quantum condensed matter physics and tests of fundamental physics, among other areas. It has been known since the early 1990s that laser cooling can, in principle, be improved by using squeezed light as an electromagnetic reservoir; while quantum feedback control using a squeezed light probe is also predicted to allow improved cooling. Here we show the implementation of quantum feedback control of a micro-mechanical oscillator using squeezed probe light. This allows quantum-enhanced feedback cooling with a measurement rate greater than it is possible with classical light, and a consequent reduction in the final oscillator temperature. Our results have significance for future applications in areas ranging from quantum information networks, to quantum-enhanced force and displacement measurements and fundamental tests of macroscopic quantum mechanics.

Bandwidth manipulation of quantum light by an electro-optic time lens

The ability to manipulate the spectral-temporal waveform of optical pulses has enabled a wide range of applications from ultrafast spectroscopy to high-speed communications. Extending these concepts to quantum light has the potential to enable breakthroughs in optical quantum science and technology. However, filtering and amplifying often employed in classical pulse shaping techniques are incompatible with non-classical light. Controlling the pulsed mode structure of quantum light requires efficient means to achieve deterministic, unitary manipulation that preserves fragile quantum coherences. Here we demonstrate an electro-optic method for modifying the spectrum of non-classical light by employing a time lens. In particular we show highly-efficient wavelength-preserving six-fold compression of single-photon spectral intensity bandwidth, enabling over a two-fold increase of single-photon flux into a spectrally narrowband absorber. These results pave the way towards spectral-temporal photonic quantum information processing and facilitate interfacing of different physical platforms where quantum information can be stored or manipulated.

Double Quantum Dot Floquet Gain Medium

Strongly driving a two-level quantum system with light leads to a ladder of Floquet states separated by the photon energy. Nanoscale quantum devices allow the interplay of confined electrons, phonons, and photons to be studied under strong driving conditions. Here we show that a single electron in a periodically driven DQD functions as a "Floquet gain medium," where population imbalances in the DQD Floquet quasi-energy levels lead to an intricate pattern of gain and loss features in the cavity response. We further measure a large intra-cavity photon number n_c in the absence of a cavity drive field, due to equilibration in the Floquet picture. Our device operates in the absence of a dc current -- one and the same electron is repeatedly driven to the excited state to generate population inversion. These results pave the way to future studies of non-classical light and thermalization of driven quantum systems.

Fully integrated quantum photonic circuit with an electrically driven light source

Photonic quantum technologies allow quantum phenomena to be exploited in applications such as quantum cryptography, quantum simulation and quantum computation. A key requirement for practical devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Nanophotonic circuits enable the realization of complex linear optical systems, while non-classical light can be measured with waveguide-integrated detectors. However, reproducible single-photon sources with high brightness and compatibility with photonic devices remain elusive for fully integrated systems. Here, we report the observation of antibunching in the light emitted from an electrically driven carbon nanotube embedded within a photonic quantum circuit. Non-classical light generated on chip is recorded under cryogenic conditions with waveguide-integrated superconducting single-photon detectors, without requiring optical filtering. Because exclusively scalable fabrication and deposition methods are used, our results establish carbon nanotubes as promising nanoscale single-photon emitters for hybrid quantum photonic devices. Single photons are generated from electrically driven semiconducting single-walled carbon nanotubes embedded in a photonic circuit. Pronounced antibunching is observed when photon correlation is measured at cryogenic temperatures.