WO2021086236A1

WO2021086236A1 - Laboratory bench for teaching and research in quantum optics and quantum information science

Info

Publication number: WO2021086236A1
Application number: PCT/RU2020/050310
Authority: WO
Inventors: Константин Григорьевич КАТАМАДЗЕ
Priority date: 2019-10-31
Filing date: 2020-10-30
Publication date: 2021-05-06
Also published as: RU2734455C1

Abstract

The invention relates to the field of optics and quantum physics and concerns a teaching and research laboratory bench for studying the polarization and correlation properties of single-photon, two-photon, coherent and thermal light fields, Hong-Ou-Mandel interference and homodyne detection. The bench comprises a pump laser module, a two-photon source module, A and B channel polarization measurement modules, a correlation measurement module, a coherent and thermal state source module, and a homodyne detection module. The two-photon source module contains a polarization controller, and non-linear crystals. The A and B channels contain two-photon radiation polarization controllers, a polarization filter and/or a beam splitter. The correlation measurement module contains single-photon detectors connected to a pulse correlator that is connected to a computer. The coherent and thermal state source module contains a laser and a beam splitter that splits light into two channels, wherein one channel has a matt disc disposed therein for the random phase and amplitude modulation of the laser radiation. The technical result lies in expanding the functional capabilities of the bench, allowing the automation of experiments, and increasing measurement accuracy.

Description

EDUCATIONAL AND SCIENTIFIC LABORATORY STAND OF THE DAY OF QUANTUM OPTICS AND

QUANTUM INFORMATICS

Technology area

The invention relates to the field of physics, namely to optics and quantum physics, and can be used to practice practical skills in the implementation of processes used in technologies of quantum communications and quantum computing, including, but not limited to, conducting the following studies: polarization and correlation properties of single-photon , biphotonic, coherent and thermal light fields, Hong-Ou-Mandel interference, and homodyne detection.

State of the art

One of the most difficult and at the same time demanded in the modern world section of physics is quantum physics. Its relevance is due to the development of quantum (especially quantum information) technologies. At the same time, the complexity of understanding the processes of quantum physics is due to the fact that its basic principles contradict the available experience, and therefore only practical experience with quantum systems can give a complete understanding of the laws of quantum physics.

Throughout the world, a physics workshop is an integral component of teaching a wide variety of areas of physics. From the prior art, various educational and scientific laboratory stands are known for conducting research on individual physical processes, but there are no stands that could comprehensively solve problems and demonstrate the basics of quantum physics, including:

1. Verification of violation of Bell's inequality,

2. Study of tomography of polarization qubits and quarts,

3. Study of tomography of one-qubit quantum processes,

4. Research of the statistics of photons,

5. Study of homodyne detection,

6. Research of quantum key distribution systems,

7. Research of a quantum random number generator,

8. Study of the Hong-Ou-Mandel interference.

In particular, from the article by F. T. Arecchi, "Measurement of the statistical distribution of gaussian and laser sources," Phys. Rev. Lett. 15, 912-916 (1965) known scheme installation that allows you to prepare various quasi-thermal and coherent states of light, and measure their intensity statistics. This scheme makes it possible to partially implement Problem 4 and 7, but in a limited version, since it does not allow preparing biphoton and one-photon fields, as well as measuring the number of photons instead of intensity. In addition, it does not allow the implementation of other tasks: 1, 2, 3, 5, 6, 8.

From S. Friberg, C. K. Hong, and L. Mandel, "Measurement of Time Delays in the Parametric Production of Photon Pairs," Phys. Rev. Lett. 54, 2011-2013 (1985), a setup scheme is known that allows solving problem 8 - the study of the Hong-Ou-Mandel interference, but it cannot solve other problems.

Closest to the proposed stand is the installation presented in the article by G. I. Stmchalin, I. A. Pogorelov, S. S. Straupe, K. S. Kravtsov, I. V. Radchenko, and S. P. Kulik, "Experimental adaptive quantum tomography of two-qubit states," Phys. Rev. A 93, 012103 (2016), with the help of which it is possible to prepare a set of different polarization states of biphotons, and to carry out their complete tomography. This scheme allows you to implement some of the above tasks (1, 2, 4, 6, 7). The setup consists of a narrow-band pump laser at a wavelength of 408 nm, optically coupled to a polarization pump controller, consisting of two phase plates (half-wave and quarter-wave at the pump wavelength), coupled by optical coupling to a pair of crossed type I nonlinear crystals, in which generation occurs biphoton field in the noncollinear mode, when one photon propagates along channel 1, and the second along channel 2. In both channels, one polarization controller is located, also consisting of two phase plates (half-wave and quarter-wave at double the pump wavelength) and along the polarization beam splitter ( Wolaston prism). Each beam splitter divides each of the channels into 2. As a result, 4 optical channels are formed, each of which is optically connected to a single-photon detector. All 4 detectors are also configured to be electrically connected to the pulse correlator.

The disadvantages of this solution include the impossibility of preparing an arbitrary biphoton state, which limits the possibilities of research in problems 2 and 6. In addition, it does not allow preparing coherent and quasi-thermal states of light, which limits the possibilities of research in problems 4, 7. Finally, it does not allow solving problems 3 and 5.

A technical problem is the development of a stand (workshop) in the form of a single modular system that allows you to implement all the above tasks with the possibility of automating the experiment and remote access to the installation.

Disclosure of invention

The technical result achieved by the claimed invention is the ability to solve key problems of quantum optics and quantum informatics, including:

1. Verification of violation of Bell's inequality

2. Tomography of polarization qubits and quarts

3. Tomography of one-qubit quantum processes

4. Photon statistics

5. Homo dom detection

6. Systems of quantum key distribution

7. Quantum random number generator

8. Hong-Ou-Mandel interference, using one stand, characterized by a modular design.

The stand allows carrying out model experiments of quantum physics with high accuracy and reproducibility of results while ensuring the convenience of research and implementation of experiments.

The technical result is achieved by creating an educational and scientific laboratory stand for researching the polarization and correlation properties of single-photon, biphoton, coherent and thermal light fields, Hong-Oy-Mandel interference, and homodyne detection, including a pump laser module located on the optical table in series with optical communication , a biphoton source module, polarization measurement modules in channels A and B, a correlation measurement module configured to connect to a data recording and analysis device (computer), as well as a source of coherent and thermal states and a homodyne detection module, where the source module is coherent and thermal states is designed to be connected by optical communication either with the modules of polarization measurements in channels A and B, or with the module homodyne detection, and the homodyne detection module is configured to connect to a data recording and analysis device (computer), while the pump laser module contains a laser with a current and temperature controller, the biphoton source module contains a polarization controller for biphoton radiation on one optical path (controller of the polarization state pumping or polarization controller), nonlinear crystals, a system for separating radiation from biphotons and pumping radiation, which in one embodiment is made in the form of a filter that transmits radiation at a wavelength of biphotons and cuts off radiation at a pumping wavelength (for example, a notch filter); channels A and B of the polarization measurement modules contain biphoton radiation polarization controllers, a polarization filter and / or a beam splitter; the correlation measurement module contains single-photon detectors connected to a pulse correlator configured to connect to a data recording and analysis device (computer); the module of the source of coherent and thermal states contains a laser connected by optical communication with a beam splitter made with the possibility of dividing light into two channels, in one of which there is a matt disk made with the possibility of rotation around its center to randomly modulate the laser radiation in phase and amplitude, both channels are made with the possibility of connecting to the polarization measurement modules and the homodyne detection module; The homodyne detection module contains a polarization beam splitter, the inputs of which are configured to connect to the outputs of the source of coherent and thermal states, and its output channel contains a polarization controller and a second polarization beam splitter, the outputs of which are optically connected to light detectors.

The biphoton radiation polarization controller in the biphoton source module and polarization measurement modules consists of sequentially located half-wave and quarter-wave phase plates installed in rotating slides. The phase plates of the polarization controller in the biphoton source module are designed for the pump laser wavelength, and the phase plates Polarization controller plates in polarization measurement modules - twice the wavelength. The biphoton radiation polarization controllers in the biphoton source module and polarization measurement modules are made on rotating slides (around the optical axis) with the ability to connect to a computer and automatically adjust the angle of rotation of the slides.

Optical fiber can be used as an optical link connecting the modules.

The laser in the pump laser module is a laser diode installed in a collimation tube with the possibility of temperature stabilization by using a Peltier element connected to a current and temperature controller. The pump laser module contains a coupler - a device for input / output of radiation into the optical fiber, which is a tube with a lens, in the focal plane of which the end of the optical fiber is located for communication with the adjacent module. In one embodiment of the invention, the pump laser module includes an optical isolator located between the laser and the coupler to prevent reflected radiation from returning to the laser. An embodiment of the pump laser module is possible, according to which a pair of prisms is installed between the laser and the coupler, made with the possibility of adjusting the shape of the beam to effectively introduce radiation into the fiber. The laser diode in the pump laser module can be configured to operate at a wavelength of 400-410 nm and has a line width of no more than 1 GHz. In a particular embodiment, the laser diode contains an embedded high-Q (eg, Bragg) resonator. In yet another embodiment of the invention, the pump laser module comprises a diffraction grating coupled to the laser diode by optical coupling to provide the required spectral width and serves as an external resonator mirror.

The module of the source of biphotons from the input side contains a coupler, in the focal plane of the lens of which the end of the optical fiber is located for connection with the pumping module, and is configured to connect to polarization measurement modules in channels A and B also using another coupler, which is configured to be connected to the module a source of coherent and thermal states (i.e. the second coupler is not included in the design of this module, acts as a separate element connections / connections of the mentioned modules). The frequency filter in the biphotone source module can be made for a wavelength of 405 nm with antireflection in the range of 400-410 nm. The nonlinear crystals in the biphoton source module are made taking into account crystallographic axes for degenerate phase matching of type I for the pump wavelength with orthogonally oriented optical axes. The biphoton source module contains a pumping frequency filter and a lens installed after the pumping frequency filter and in front of the nonlinear crystals so that the crystals are in its focus, while the lens is made with an antireflection coating at the pumping wavelength. In one embodiment of the invention, the biphoton source module contains a second lens installed behind the nonlinear crystals and a second frequency filter installed behind the second lens, while the second lens is installed so that the crystals are in its focus, and is made with an antireflection coating on a double pump wavelength, and the second frequency filter is made to transmit biphotons radiation at the double pump wavelength, but does not transmit radiation at the pump wavelength.

The laser of the module of the source of coherent and thermal states is connected to the beam splitter using an optical fiber, has a fiber output, its spectrum width does not exceed 1 MHz, and the center wavelength is equal to twice the pump laser wavelength. The matt disk of the module of the source of coherent and thermal states is connected to the output of the beam splitter and to the output optical fiber by means of couplers. The matt disk of the module of the source of coherent and thermal states is made with the possibility of connecting to a computer and adjusting the rotation speed, including full stop.

The connection of the biphoton source module and the coherent and thermal state source module to the polarization measurement modules in channels A and B is realized by means of a beam splitting plate having two inputs and two outputs, one of the inputs is connected to the output of the biphoton source module, the second input is connected to the output of the module source of coherent and thermal states through the coupler, and the outputs of the beam splitting plate are optically connected to the inputs of the polarization measurement modules in channels A and B.

Modules for polarization measurements in channels A and B contain couplers located at the output of the modules, through which a fiber-optic connection with the correlation measurement module is realized, while in front of the couplers Narrow-band frequency filters with a transmission range of 10-40 nm are installed, the center of the transmission range of which coincides with the doubled wavelength of the pump laser. One of the couplers of the polarization measurement module in channel A is installed on a translational slide made with the ability to change the distance between it and the polarization filter and / or beam splitter, while the translational slide can be connected to a computer.

The correlation measurement module contains four single-photon detectors, the optical inputs of which are connected to the optical outputs of the polarization measurement modules, while two of the four detectors are connected to the outputs of channels A and B through a symmetric (single-mode) fiber-optic beam splitter. The pulse correlator is configured to count the number of photocounts for each channel, as well as measure the number of coincidences of photocounts between any two channels and measure the histogram of the delay times between pulses traveling along any of the two channels.

The homodyne detection module is equipped on the input side with couplers for connection by means of optical fibers to the module of the source of coherent and thermal states. The polarization controller in the homodyne detection module is made in the form of a half-wave phase plate for twice the pump wavelength. The homodyne detection module also contains an analog-to-digital converter (ADC) unit connected to the light detectors and adapted to be connected to a computer. The light detectors in the homodyne detection module are made in the form of a single module that includes a differential photocurrent amplifier. In one embodiment of the invention, in front of the first polarizing beam splitter of the homodyne detection module, a mirror is installed on a precision piezo-slider connected to a sawtooth signal source; and a long-focus lens is installed in front of the second polarizing beam splitter of the homodyne detection module, with the detectors located from the lens at its focal length.

In one embodiment of the invention, the educational and scientific laboratory stand contains a computer connected to the stand modules, made with the possibility of remotely connecting another computer with the possibility of remote control of all the stand modules. In the claimed invention, for fiber-optic connection of modules, it is preferable to use kaylers - devices for input / output of radiation into an optical fiber, which is a tube with a lens, in the focal plane of which the end of the fiber is located. Thus, the achievement of the technical result is ensured due to the fact that several universal modules are combined in one optical scheme: modules of a pump laser, a source of biphotons, a source of coherent and thermal states, two modules of polarization measurements, a module of correlation measurements and a module of homodyne detection. To be able to solve a wide range of quantum physics problems using one modular stand, a scheme was developed that includes the minimum necessary and sufficient set of devices and structural elements with the ability to connect elements in a module and modules to each other for the task being solved. These modules can be switched with each other in different ways and their parameters can be set depending on the specific task. At the same time, in order to increase the number of students at the same time, most of the modules can be automated and can be accessed remotely. The interface of the remote access programs creates the effect of full presence for the user due to the multitude of sensors and webcams.

Brief Description of the Drawings The invention is illustrated by the drawing, which shows a diagram of the developed stent.

The positions in the drawing indicate:

1, 6 - laser diode,

1a, 6a - current and temperature controller for a laser diode, 2 - a diffraction grating for creating an external resonator to diode 1,

3 - optical Faraday isolator,

4 - a pair of anamorphic prisms for transforming the beam profile of diode 1,

5a, 5b, 9, 9a, 11, 32, 33, 34, 35, 63, 64 - single-mode polarization-saving fiber (optical fiber), 7 - single-mode fiber beam splitter (polarization-saving beam splitter),

8 - radiation attenuator,

10 - rotating matte disc,

12 - polarizer for laser radiation, 13 - half-wave plate of zero order with antireflection,

14 - zero-order quarter-wave plate with antireflection,

15 - bandpass filter,

16 - dichroic mirror, 17, 60 - plane-curved lens with antireflection coating,

18 - a pair of crossed BiBO crystals,

19 - flat-curved lens with antireflection coating,

20 - notch filter,

21 - 50:50 beamsplitter, 22, 24, 26, 28, 59 - zero-order half-wave plate with antireflection,

23, 25, 27, 29 - zero-order quarter-wave plate with antireflection,

30, 31, 58, 61 - polarizing beam splitter cube for radiation (polarizing beam splitter),

36, 37, 38, 39 - silicon single-photon detector,

40, 41, 42 - interference filter,

43 - motorized translational movement,

44 - single-mode fiber beam splitter (polarization-preserving beam splitter),

45 - correlator for processing pulses coming from detectors 36-39, including 4 "start-stop" circuits,

46, 67 - device for recording and analyzing data (computer or personal computer), 47-57 - devices for input / output of radiation into optical fiber (couplers),

62 - balanced detector,

65 - piezo mirror,

66 - analog-to-digital converter.

DETAILED DESCRIPTION OF THE INVENTION Educational and scientific laboratory stand for researching the polarization and correlation properties of single-photon, biphoton, coherent and thermal light fields, Hong-Oy-Mandel interference and homodyne detection, includes a pump laser module located on an optical table, connected by optical communication with the module source of biphotons, optically connected to the polarization measurement modules in channels A and B, optically connected to the correlation measurement module, which in turn is configured to be connected to a data recording and analysis device (computer), as well as a coherent and thermal state source module made with the ability to connect by optical communication either with the modules of polarization measurements in channels A and B, or with a homodyne detection module, which is also configured to be connected to a data recording and analysis device (computer).

The pump laser module is a current and temperature controller 1 a connected to a laser diode 1 installed in a collimation tube in thermal contact with a Peltier element, also connected to a current and temperature controller. The laser diode 1 is optically connected to an optical isolator 3, which is then connected to a module for input / output of radiation into an optical fiber (coupler) 47, which is a tube with a lens, in the focal plane of which the end of the optical fiber 5 a is located.

Laser diode 1 in the pump laser module operates at a wavelength of 400-410 nm and has a line width of no more than 1 GHz. For this, either a laser diode with a built-in high-Q (for example, Bragg) resonator is used as a laser diode 1, or a diffraction grating 2 is installed in the optical connection connecting the laser diode 1 with the optical isolator 3.

To increase the fraction of laser radiation introduced into the optical fiber in the pump laser module, a pair of prisms that correct the beam shape (not shown in the drawing) can be placed in the optical link connecting the optical isolator 3 with the optical fiber.

The biphoton source module consists of a coupler 48, in the focal plane of the lens of which the end of the optical fiber 5b is located, which is optically connected to a polarizer 12, which is optically coupled to a half-wave phase plate 13, designed for a wavelength of 405 nm and antireflection in the range of 400-410 nm, connected optical communication with a quarter-wave phase plate 14, designed for a wavelength of 405 nm and antireflection in the range of 400-410 nm, coupled by optical communication with a spectral filter 15 that transmits radiation in the range of 400-410 nm, coupled by optical communication with a lens 17, in the focus of which there is a pair of nonlinear crystals 18 cut under degenerate phase-matching of type I for the pump wavelength, the optical axes of which are oriented orthogonally. If the crystals are cut for collinear synchronism, then the crystal is connected by one optical connection with the lens 19 connected to the spectral filter 20, blocking radiation at a wavelength of 400-410 nm and transmitting at a wavelength of 800-820 nm, connected to the input of a symmetric non-polarization beam splitter 21, the outputs of which are optically connected to the polarization measurement modules in channels A and B. In this case, the other input of the beam splitter 21 is optically connected to the coupler 53 in the focal plane of the lens of which the end of the fiber 11 is installed, the other end of which can be connected to the module source of coherent and thermal states. If the crystals are cut for non-collinear synchronism (not shown in the diagram), then the crystal is connected by one optical connection with a lens connected to a spectral filter that blocks radiation at a wavelength of 400-410 nm and transmits at a wavelength of 800-820 nm, connected by optical communication with the polarization measurement module in channel A, and another optical communication with a lens connected to a spectral filter blocking radiation at a wavelength of 400-410 nm and transmitting at a wavelength of 800 - 820 nm, connected by optical communication with a polarization module measurements in channel B. In this case, the coupler 53 is optically connected to nonlinear crystals 18 located on the same optical axis with the coupling between the crystals and one of the polarization measurement modules. Phase plates 13, 14 are installed in rotating slides with the ability to connect to a control device (computer).

The module of the source of coherent and thermal states consists of a narrow-band laser diode 6 with a fiber output, a spectrum width of no more than 1 MHz and a center wavelength twice as long as the wavelength of a pump laser connected by an optical fiber to a fiber beam splitter 7, the first fiber output of which 9 has the ability connection to the homodyne detection module, and the end of the fiber of the second output 9a is at the focus of the lens of the fiber coupler 54, optically connected to the rotating matt disk 10, which is optically coupled to the coupler 55, in the focal plane of the lens of which the end of the fiber 11 is located, the second end of which is has the ability to connect to polarization measurement modules in channels A and B.

The connection of the source of biphotons and the source of coherent and thermal states to the modules of polarization measurements in channels A and B is provided as follows: the output connector of the optical fiber of the source of coherent and thermal states is connected to optical fiber 11, the second end of which is at the focus of the lens of the coupler 53, which is optically connected to the input symmetric beam splitter 21. The second input of the beam splitter is optically connected to the output of the biphoton source. The outputs of the beam splitter are optically connected to the inputs of the polarization measurement modules in channels A and B.

The input of the polarization measurement module in channel A is optically connected to a half-wave plate 22 at 810 nm with an antireflection coating for the 800-820 nm range, installed in a rotating slide connected by optical coupling to a quarter-wave plate 23 at 810 nm with an antireflection coating for the range 800-820 nm, installed in a rotating slide, optically coupled to a half-wave plate 24 at 810 nm with an antireflection coating for the range of 800-820 nm, installed in a rotating slide, connected by optical communication with a quarter-wave plate 25 at 810 nm with an antireflection coating for a range of 800-820 nm, installed in a rotating slider, optically connected to a polarizing beam splitter 30, one of the outputs of which is optically connected to an interference filter 40a, which transmits radiation only in the 800-820 nm range, optically connected to a coupler 49, in the focus of the lens of which an optical fiber is located 32 s possible connection to the module of correlation measurements; the second output of the polarizing beam splitter 30 is optically connected to an interference filter 40 that transmits radiation only in the 800-820 nm range, optically connected to a coupler 50, in the focus of the lens of which an optical fiber 33 is located, with the possibility of connecting to a correlation measurement module; coupler 50 is installed on the translational slide with the ability to connect to a control device (computer). Phase plates 22-25 are installed in rotating slides with the ability to connect to a control device (computer). The input of the polarization measurement module in channel A is optically connected to a half-wave plate 26 at 810 nm with an antireflection coating for the 800-820 nm range, installed in a rotating slide connected by optical coupling to a quarter-wave plate 27 at 810 nm with an antireflection coating for the range 800-820 nm, installed in a rotating slide, optically connected to a half-wave plate 28 at 810 nm with an antireflection coating for the range of 800-820 nm, installed in a rotating slide, connected by optical communication to a quarter-wave plate 29 at 810 nm with an antireflection coating for a range of 800-820 nm installed in a rotating slider, optically connected to a polarizing beam splitter 31, one of the outputs of which is optically connected to an interference filter 41 that transmits radiation only in the 800-820 nm range, optically connected to a coupler 51, in the focus of the lens of which an optical fiber is located 34 s possible connection to the module of correlation measurements; the second output of the polarizing beam splitter 31 is optically connected to an interference filter 42 that transmits radiation only in the 800-820 nm range, optically connected to a coupler 52, in the focus of the lens of which an optical fiber 35 is located, with the possibility of connecting to a correlation measurement module; phase plates 26-29 are installed in rotating slides with the ability to connect to a control device (computer).

The correlation measurement module consists of four single-photon detectors 36-39, the optical inputs of which are connected to the outputs of the optical fibers of the polarization measurement modules 35-32, respectively. In the case of investigating the Hong-Ou-Mandel interference, fibers 34, 33 are connected to detectors 37, 38 through a fiber beam splitter 44. The electronic outputs of detectors 36-39 are optically connected to a pulse correlator 45, which has the function of counting the number of photocounts for each channel, as well as measuring the number of coincidences of photocounts between any two channels and measuring the histogram of the delay times between pulses traveling along any of the two channels. The correlator output can be connected to a data analysis and processing device (computer) 46. The homodyne detection module consists of optical fibers 63, 64, the inputs of which can be connected to the outputs of optical fibers 9 and 11 of a source of coherent and thermal states. The second ends of the fibers 63, 64 are located in the focal planes of the lenses of the kaylers 56, 57, which are optically connected to the inputs of the polarizing beam splitter 58, the output of which is optically connected to a half-wave plate 59 at 810 nm with an antireflection coating for the 800-820 nm range installed in a rotating slide, optically connected to the lens 60, optically connected to a polarizing beam splitter 61, the outputs of which are connected to the inputs of the balanced detector 62, configured to measure the signal intensities in each channel separately and the intensity difference between the channels. On the optical link between the coupler 57 and the polarizing beam splitter 58, there can be a mirror 65 mounted on a piezo slider. The detector 62 is placed so that its optical inputs are in the focus of the lens 60. The detector 62 is electrically connected to an analog-to-digital converter 66 (ADC ) with the ability to connect to a data analysis and processing device (computer) 46.

A feature of the claimed invention is that the coupler 50, which introduces radiation into the optical fiber, connected to one of the detectors of the correlation measurement module, can be installed on the translational slide, and two detectors can be connected to optical channels through a beam splitter, which makes it possible to observe the Hong-Oy interference -Mandel (task 8). In addition, not one, but two polarization converters are installed in each channel, which makes it possible to prepare and measure any one-photon and biphoton quantum states, which makes it possible to fully implement Problems 2, 3, 6. The presence of a source of coherent and quasi-thermal states, as well as a module homodyne detection, allow to fully implement tasks 4, 5 and 7.

Below is a detailed description of the work of the stand when solving the above problems of quantum physics.

The pump source for the process of spontaneous parametric scattering is a laser diode 1 emitting at a wavelength of 400-410 nm. The diode current and temperature are stabilized by controller 1a. Laser radiation collimated by the lens and directed to the diffraction grating 2, set in such a way that the maximum of the first order is reflected back into the laser. Due to this, an external resonator with a higher selectivity is formed, which makes it possible to significantly narrow the radiation spectrum. The zero-order maximum is reflected from the grating and enters the optical isolator 3, which protects the laser diode from back illumination, and a pair of anamorphic prisms 4, which convert the elliptical section of the beam into a circular one. Then, by means of a coupler 47, the pump radiation is introduced into the optical fiber 5a. All optical fibers used are single-mode and polarization-retaining.

In addition to the pump laser, the system contains a source of coherent and thermal states of light. It is based on a diode laser 6 with a fiber optic output for radiation with a wavelength of 810 nm. The current and temperature of the laser diode are also stabilized by the controller 6a. This radiation is divided by a fiber beam splitter 7 into two parts: the first, coherent, is transmitted into fiber 9, and the second is focused on the rotating matt disk 10 and, after dephasing, enters fiber 11. Thus, at the output of the source, coherent and thermal states are output through fiber 9 a powerful coherent state used as a homodyne, and at the output of fiber 11 - a thermal state if the matt disk rotates, and a weakened coherent state if the disk is stopped.

To generate biphotons, the pump laser radiation is extracted from fiber 5b, collimated by a coupler lens 48, passed sequentially through polarizer 12, a pair of phase plates (quarter-wave plate 14 and half-wave plate 13 oriented at angles f and q _p to the vertical, respectively), which set the polarization state of the pump , a narrow-band filter 15 that transmits the laser radiation line, and then is focused by a lens 17 on an assembly 18 of two nonlinear BiBO crystals with a thickness of 0.5 mm. The crystals are cut at an angle of collinear degenerate phase-matching of type I, their axes are rotated so that in the first crystal, under the action of vertically polarized pumping, pairs of photons with a horizontal polarization plane HH are produced, and in the second, on the contrary, under the action of horizontally polarized pumping, pairs of vertically polarized photons | W). In the general case, the quantum state of biphotons at the output has the form with _hn \ HH + C _yy \ w), for which the amplitude ratio of the modules | with _Yaya | / | c _yy | is determined by the angle q and the phase difference

The radiation generated in the crystals 18, containing biphotons, is collimated by the lens 19, and the pump radiation is absorbed by the filter 20. Then, the radiation of the biphotons is divided by a beam splitter 21 (insensitive to polarization) into two channels "A" and "B". It should be noted that in this case, with a probability of 1/2, the photons will not split and leave in one channel, but by highlighting the cases when one photon is recorded in each of the channels, it is possible to cut off the cases when the photons did not split. In some problems, instead of emitting biphotons, coherent and thermal states of light are used, which enter the system through optical fiber 11, are collimated by the lens of the kayler 53 and are fed to the second input of the beam splitter 21.

Each channel has a pair of phase plates (quarter-wave 23, 27 and half-wave 22, 26, set at angles f _Al , f _m , q _A1 and q _m , respectively), which together with the plates controlling the pumping (13 and 14) allow prepare an arbitrary pure polarization state of a biphoton of the form c _HH \ H) _A \ H) _B + c _HV \ H) _A \ v) _B + C _yH \ v) _A \ H) _B + C _yV \ v) _A \ v) _B ... Then in each channel is set by another pair of plates (quarter-wave 25, 29 and half-wave 24, 28, mounted at angles f _A2 / _B2, q _A2 and q _B2, sotvetstvenno) and polarizing beam splitters 30, 31, skipping vertically polarized photons, and reflective horizontally polarized. The angles of rotation of the phase plates determine the measuring basis, that is, the type of measurement operators

^and

^l 1v ^{in each} D ° ^m channel. In each output channel of the beam splitters, the radiation is focused by couplers 49-52 into fibers 32-35 connected to single-photon detectors 39-36. In front of the entrance to each fiber, narrow-band filters 40, 40a, 41, 42 are installed, which transmit the radiation of biphotons, as well as thermal and coherent states of light at a wavelength of 810 nm, and cut off the illumination. The coupler 50, which focuses the radiation into the fiber 33, is mounted on the translational slide 43, which makes it possible to measure the Mandel dip. In this case, fibers 33 and 34 are connected to detectors 37 and 38 through a fiber beam splitter 44. All detectors are connected to correlator 45, which allows registering the number of photocounts in each channel and the number of matches between any pair of channels. The result is sent to the computer. In the automated version, the positions of all phase plates, as well as translational shifts 43, are set from a computer.

In the "Homodyne detection" problem, the fibers of the source of coherent and thermal states 9 and 11 are connected to fibers 63 and 64 of the homodyne detection module. The polarization-retaining fibers 9, 11, 63, 64 are oriented such that the output radiation collimated by the droppers 56 and 57 is orthogonally polarized. Then the homodyne radiation propagating along the fibers 9 and 63 and the radiation of the investigated field propagating along the fibers 11 and 64 are knocked down on the polarizing beam splitter 58 into one spatial mode, then they are rotated from polarization by 45 degrees by a half-wave plate 59, and are again divided symmetrically into two channels polarizing beam splitter 61, each of which is focused with a lens 60 into the optical input of the balanced detector 62, which measures the intensity difference in the input channels. To change the relative phase between the homodyne and the radiation under study, a mirror on the piezo-slider 63 is installed in the optical channel between the coupler 57 and the beam splitter 58. 1. The problem of verifying the violation of Bell's inequality is solved as follows.

The angles of rotation of the control phase plates /, q _p , f _Al , f _m , q _A1 and q _m are set so that the generation of biphotons occurs in a maximally entangled state, for example, in one of the Bell states: l ^F 0 = (l ⁱⁱ L | H> _B ^± l ^ l ') ") / ^ ^{2 and} ™ l ^Y 0 = (HJ ^l I ^F ) J") _s ) / 2 ^. Then determine two sets of angles of the measuring phase plates / _A A ¹ , / ^ ' ₂ ²¹ , SC ²⁾ and Chv? _> For which the value of the Bell variable y takes the maximum

value. Then the Bell variable is measured and the statistical error of the measurement result is estimated. It is important to make sure that

2.

2. Investigation of tomography of polarization qubits and quarts is carried out as follows. The angles of rotation of the control phase plates /, q, f _Al , f _m , q _A1 and q _Bl are set in such a way that the generation of biphotons occurs in a maximally entangled state, for example, in a given state:

Select some measurement protocol - a set of measurement operators

J, {D ° J, and for each combination of operators for a certain fixed time the number of events corresponding to each of the four outcomes is measured. The result is written to a file. This file is then processed on a computer using the maximum likelihood method with quantum state restoration. The restored state is compared with the preset one and the fidelity is calculated. In this case, several options for tasks are possible:

- The initial two-photon (two-qubit) state is factorized, then the state of the polarization qubit in each channel is clean. The results of measurements of only one qubit are analyzed, and on their basis, the pure state is restored.

- For the same dataset, the qubit state is reconstructed as mixed and its purity is assessed.

- The initial two-qubit state is entangled, then the state of the qubit in each channel is mixed. Based on the measurement results, the mixed state of the qubit is reconstructed.

- Analyze the full amount of data for a two-qubit state, for both factorized and entangled states. In each case, the state of both clean and entangled is assessed.

- For each of the tasks, the dependence of fidelity on the sample size can be estimated.

3. The study of tomography of one-qubit quantum processes is carried out as follows.

The angles of rotation of the control phase plates /, q _p , f _Al , f _m , q _A1 and q _m are set in such a way that the generation of biphotons occurs in the factorized state: \ n _A \ n _c. The photon in the "A" channel is used as a trigger, and in the "B" channel - for the tomography of the quantum process. The quantum process is realized with some polarizing element installed between phase plates 27 and 28. For imaging quantum process a set of input prepared quantum states (by selecting different angles f _m and q _B1), and produce a set of measurements (by selecting different angles f _c2 and q _B2) for each output condition.

The measurement results are written to a file, and then the unitary matrix, or chi-matrix, describing the quantum process, is reconstructed.

4. The problem of quantum key distribution is solved as follows.

This setup allows the implementation of various quantum key distribution protocols. The following is a description of the three options.

Option 1. Protocol BB84 (version 1). The angles of rotation of the control phase plates /, q, f _Al , f _t , q _A1 and q _B1 are set in such a way that the generation of biphotons occurs in the factorized state: \ n _A \ n _c. Photon in the channel

"A" is used as a trigger, and in channel "B" - for key transmission. In this case Alice prepares a quantum state of a photon, by setting the angles / _m and q _B1, and Bob chooses a measuring basis, setting position and the plates f _c2 q _B2. A sequence of random key bits, a sequence of Alice's bases and a sequence of Bob's bases are generated in advance. The key is transferred, the data is written to a file. Analyze the data obtained: sifting the key, analyzing the percentage of errors. Similarly, you can implement other one-pass protocols, for example, B92. Optionally, you can also introduce interference into the communication channel related to the actions of Eve. For example, put a polarizer between the phase plates 27 and 28, the rotation angle of which is also randomly selected. To speed up the key transfer process, you can simply sequentially iterate over all combinations of the angles of rotation of Alice's and Bob's plates, obtain a separate data set for each set, and then mix them in accordance with the sequence in which Alice's random states and Bob's random bases go.

Option 2. Protocol BB84 (version 2). The angles of rotation of the control phase plates /, q _p , f _Al , f _Bl , q _Al and q _m and are set so that the generation of biphotons occurs in an entangled state. In this case, Alice's station is answered by channel "A", and Bob's station is answered by channel "B". Alice and Bob measuring bases are randomly selected, and measurements are carried out. The measurement results are written to a file and analyzed in the same way as it was done in the previous paragraph. Other single-pass protocols can be implemented in the same way.

Option 3. Eckert's protocol. The setup parameters are the same as in the previous paragraph, but Alice and Bob choose the measurement bases in such a way that, in parallel with the key distribution, it is possible to measure Bell's inequalities. Accordingly, when processing data, in addition to the key and errors, it is also necessary to make sure that Bell's inequalities are violated.

5. Investigation of the statistics of photons is carried out as follows.

This problem is devoted to the study of the statistics of photocounts of various quantum states of light: one-photon, two-photon, coherent, thermal.

1. Coherent state of light. The pump laser is turned off (blocked), the coherent state of light from the red laser is fed to the input of the system. Only channel "A" is used for analysis.

1L. The measurement of the autocorrelation function is carried out using two detectors. The angles of the phase plates f _Al , q _A1 , f _A2 and q _{A2 are} set so that the count rate of the detectors 38 and 39 is the same. The signals from these detectors are sent to the start-stop circuit, the stop events pass through the electronic delay line, and the histogram of the times between the start and stop events is measured.

1.2. Measurement of the autocorrelation function using a single detector. The angles of the phase plates f _Al , q _A1 , f _A2 and q _{A2 are} set so that the count rate of the detector 39 is maximum. The signals from this detector are sent to the start-stop circuit, thus measuring the histogram of times between adjacent pulses. By changing the angles f _Al , q _Al , f _A and q _A2, you can change the photon count rate in the channel, and take histograms for its different values.

1.3. Measurement of higher-order autocorrelation functions. The angles of the phase plates / _A1 , q _A1 , f _A2 , q _A2 , f _m , q _m , f _b2 ,

set so that the count rate of all four detectors is the same. For some time, the number of single photocounts in each channel is measured, as well as the number of double, triple and quadruple coincidences. Calculate the values of the correlation functions of the second, third and fourth order at zero.

1.4. Measurement of the distribution by the number of photons. The angles of the phase plates f _A1 , L \ 'f _A 2 ^and FM are set in such a way that the count rate of the detector 39 is maximum. One input "start" of the start-stop circuit is fed with a periodic signal with a period of 1-10 ms. Stop signals from detector 39 are applied to the input. A set of measurements of the number of photocounts is made for some fixed accumulation time, determined by the coincidence circuit window. A histogram of the number of photocounts (coincidences) is built, reflecting the distribution by the number of photons. You can build histograms for different values of the accumulation time. By changing the angles / _A1 , q _A1 , f _A2 and q _A2, you can change the photon count rate in the channel and take histograms for its different values.

1.5. Implementation of photon splitting. The angles of the phase plates f _Al , q _A1 , f _A2 and q _{A2 are} set so that the average number of photons over a fixed accumulation time recorded by the detector 38 is 0.1. The correlator uses two start-stop circuits simultaneously. A periodic signal with a period of 1-10 ms is supplied to the "start" input of both circuits. Pulses from detector 39 are fed to the stop input of one circuit, and pulses from detector 38 are fed to the other. A set of measurements of the number of photocounts of each of the detectors is made for a certain fixed accumulation time determined by the coincidence circuit window. A histogram of the number of photocounts of the detector 39 is plotted, corresponding to the initial distribution by the number of photons, and a histogram of the photocounts of the DAH detector, provided that one photon is detected by the detector 38, a conditional distribution corresponding to the splitting off of one photon. It can be shown that for a coherent state, the splitting off of a photon does not affect the form of the distribution.

2. Thermal states of light. The pumping laser is turned off (blocked), the thermal state of the light from the red laser transmitted through the rotating matt disk is fed to the input of the system. Only channel "A" is used for analysis.

2.1. Measurement of the autocorrelation function using two detectors. The angles of the phase plates f _Al , q _Al , f _A2 and q _{A2 are} set so that the count rate of the detectors 38 and 39 is the same. Signals from these detectors the circuit is sent to the start-stop, the “stop” events pass through the electronic delay line, and the histogram of the times between the “start” and “stop” events is measured. The correlation time is measured. Several measurements can be taken by changing the rotation speed of the matte disc.

2.2. Measurement of the autocorrelation function using a single detector. The angles of the phase plates / _A1 , q _A1 , f _A2 and q _{A2 are} set so that the count rate of the detector 39 is maximum. The signals from this detector are sent to the start-stop circuit, thus measuring the histogram of times between adjacent pulses. By changing the angles f _Al , q _Al , f _L2 and q _A2, you can change the photon count rate in the channel and take histograms for different values.

2.3. Measurement of higher-order autocorrelation functions. Angles phase plates / _A1, q _A1, / _A2, q _A2, / _r, q _Bl, f _c2, q _B2, is set so that the counting rate of the four detectors is the same. For some time, the number of single photocounts in each channel is measured, as well as the number of double, triple and quadruple coincidences. Calculate the values of the correlation functions of the second, third and fourth order at zero.

2.4. Measurement of the distribution by the number of photons. The angles of the phase plates f _A1 , _{L \} 'f _A2 ^and FM are set in such a way that the count rate of the detector 39 is maximum. One input "start" of the start-stop circuit is fed with a periodic signal with a period of 1-10 ms. At the input stop - signals from the detector 39. A set of measurements of the number of photocounts is made for some fixed accumulation time, less than the correlation time determined by the coincidence circuit window. A histogram of the number of photocounts (coincidences) is built, reflecting the distribution by the number of photons. You can build a histogram for different accumulation times. By changing the angles f _Al , q _Al , f _l2 and q _A2, you can change the photon count rate in the channel, and take histograms for its different values.

2.5. Implementation of photon splitting. The angles of the phase plates / _Al , q _A1 , f _A2 and q _{A2 are} set so that the average number of photons for a fixed accumulation time is less than the correlation time recorded by the detector 38 was 0, 1. Two start-stop circuits are used simultaneously in the correlator. A periodic signal with a period of 1-10 ms is supplied to the "start" input of both circuits. Pulses from detector 39 are fed to the stop input of one circuit, and the other - pulses from the detector 38. A set of measurements of the number of photocounts of each of the detectors is made for a certain fixed accumulation time determined by the coincidence circuit window. A histogram of the number of photocounts of the detector 39 is constructed, corresponding to the initial distribution by the number of photons, and a histogram of the photocounts of the detector 39, subject to the registration of one photon by the detector 38, a conditional distribution corresponding to the splitting off of one photon. It can be shown that for the thermal state, the splitting off of photons significantly changes the shape of the distribution and doubles the average value.

3. Conditional one-photon state. The red laser (810 nm) is turned off, the pumping laser is turned on. The angles of rotation of the control phase plates /, q, f _M , f _m , q _M and q _Bl are set so that the generation of biphotons occurs in a factorized state: \ n | //). The photon in channel "B" is used as a trigger, so the conditional one-photon state in channel "A" is investigated in this way. Angles phase plates f _{_m,} q _m, f _c2 and q _B2 is set so that the count rate of the detector 36 is a maximum. Due to the fact that both photons could go into the same channel, as well as due to other optical losses, the conditional state of light in channel "A" will also have an admixture of the vacuum state.

3.1. Measurement of the time mode of the conditional one-photon state based on the measurement of the second-order correlation function. The angles of the phase plates f _{A \} , q _{, \\} - f _A 2 ^{and c} _{\ 2 are} set in such a way that the count rate of the detector 39 is maximum. The signal from the detector 36 is connected to the “start” input of the start-stop circuit, and the signal from the detector 36 is connected to the “stop” input. The histogram of the times between the “start” and “stop” events is measured. Determine the width of the histogram.

3.2. Measurement of the autocorrelation function using a single detector. The angles of the phase plates / _A1 , q _A1 , f _A2 and q _{A2 are} set so that the count rate of the detector 39 is maximum. The signals from this detector are sent to the start-stop circuit, thus measuring the histogram of times between adjacent pulses. Optionally, the same distributions can be measured provided that a photon is detected in the conjugate channel by detector 36.

3.3. Measurement of the autocorrelation function using three detectors. The angles of the phase plates f _Al , q _Al , f _A2 and q _{A2 are} set in such a way that the count rate of detectors 38 and 39 was the same. The signals from these detectors are sent to the start-stop circuit, the stop events pass through the electronic delay line, and the histogram of the times between the start and stop events is measured. In this case, events are recorded under the condition that another start-stop circuit is triggered, registering the coincidence of photocounts between detectors 39 and 36. The depth and width of the dip of the correlation function are determined.

6. The solution of the problem related to the research of the quantum random number generator is carried out as follows.

Since quantum processes are fundamentally non-deterministic, it is the quantum random number generator that will be maximally protected from possible prediction of its outcomes. This scheme allows many different quantum random number generators to be implemented. They are based on the properties of coherent radiation. The pump laser is turned off (blocked), the coherent state of light from the red laser is fed to the input of the system. 1. The angles of the phase plates / _A1 , q _A1 , f _A2 , q _A2 , f _m , q _m , f _B2 , q _B2 , are set so that the count rate of all four detectors is the same. Two bits of information are generated in one clock cycle. In each cycle, the measurement continues until at least one photon is registered by any of the four detectors. Then, depending on which detector triggered, record a number from 0 to 3. Measurements are repeated until a sufficiently large sequence of random numbers is generated. Then this sequence is written to a file, post-processed and verified.

2. The angles of the phase plates / _A1 , q _Al , f _A2 and q _{A2 are} set so that the count rate of the detector 39 is maximum. The signals from this detector are sent to the start-stop circuit, thus measuring the times between adjacent pulses. The sequence of these times also plays the role of a sequence of random numbers. Then this sequence is written to a file, post-processed and verified.

7. The problem of the Hong-Ou-Mandel interference is solved as follows.

The angles of rotation of the control phase plates f, q _{p are} set so that the state of light after a pair of crystals has the form d НН) - \ w) / f2 = (DA) + \ AD) ^' ) / f2, where the states \ D) = ( n) + \ v)) / yf2 and | A) = (I H) - | \ /) / A / 2 correspond to the diagonal and antidiagonal polarization of the photon. Then the state in channels "A" and "B" will have the form

plates / _A1, q _M, f _A2 and q _A2 is set so as to diagonally polarized photon went into fiber 33, and the angles f _{_m,} q _m, f _c2, q _{B2 -} so that antidiagonal polarized photon sign into the fiber 34 Fibers 33 and 34 are connected to detectors 37 and 38 through a fiber beam splitter 44. The number of coincidences of photocounts between detectors 37 and 38 is measured, depending on the position of translational slider 43. At a certain position of the slider, a coincidence failure will be observed - Mandel's dip.

You can measure the width of the notch depending on the bandwidth of the filters 40, 41, 42.

It is also possible to change the angles of the phase plates f _Al , q _Al , f _A2 and q _A2 so that an antidiagonally polarized photon enters the fiber 33. In this case, instead of a dip in coincidence, a peak will be observed.

8. The problem of homodyne detection is solved as follows.

The source of thermal and coherent states is connected to the homodyne detection module. Investigate the dependence of the difference intensity recorded by the detector 62 on time and on the homodyne phase as a function of the rotational speed of the matt 10.

All of the above studies were carried out on an educational and scientific laboratory bench, which was made according to the scheme shown in the drawing. In this case, the element base presented in the listed Internet sources was used: laser diode 1 with a wavelength of 405 nm (https://www.thorlabs.com/thorproduct.cfm?partnumber=L405P150); current and temperature controller 1a for laser diode 1

(https://www.thorlabs.com/thorproduct.cfm7partnumberMTC102); diffraction grating 2 for creating an external resonator to diode 1, 1200 lines / mm (https://www.thorlabs.com/thorproduct.cfm?partnumber=GR25-1204); optical Faraday isolator 3 at a wavelength of 405 nm

(https://www.thorlabs.com/thorproduct.cfm7partnumberMO-3D-405-PBS); pair of anamorphic prisms 4 to convert the beam profile of diode 1

(https: //www.thorlabs.com/thorproduct.cfm? partnumber = PS 873 -A); singlemode polarization-preserving fiber 5a, b at 405 nm

(https://shop.ozoptics.com/qpmj-3a3a-400-3125-3-l-l); laser diode 6 with a wavelength of 810 nm (https://www.thorlabs.com/thorproduct.cfm?partnumber=L808P200); current and temperature controller 6a for laser diode 6 (https://www.thorlabs.com/thorproduct.cfm7partnumberfTC 102); single-mode polar isation-conserving fiber beam splitter 7 at 810 nm; single-mode polarization-storing fiber 9 and 11 at 810 nm (https://shop.ozoptics.com/pmj-3a3a-850-5125-3-l-l); a rotating matte disc 10, with a characteristic matting grain size of 30 microns, a diameter of 5-15 cm, a thickness of 0.5-2 mm, a rotation frequency of 0 to 10 rev / s; polarizer 12 for radiation at a wavelength of 405 nm

(https://www.thorlabs.com/thorproduct.cfm?partnumber=LPVISE100-A); half-wave plate 13 of the zero order with antireflection at a wavelength of 405 nm (https://www.thorlabs.com/thorproduct.cfm?partnumber=WPH10E-405); quarter-wave plate 14 of the zero order with antireflection at a wavelength of 405 nm (https://www.thorlabs.com/thorproduct.cfm?partnumber=WPQ10E-405); bandpass filter 15 at 405 nm with 10 nm FWHM

(https://www.thorlabs.com/thorproduct.cfm?partnumber=FB405-10); mirror 16a, 16b, reflecting in the 780-850 nm range (https://www.thorlabs.com/thorproduct.cfm?partnumber=BBl-E03); lens 17 flat-curved with antireflection at 405 nm, focal length 40 mm (https://www.thorlabs.com/thorproduct.cfm?partnumber=LA4306-A); a pair of crossed BiBO 18 crystals, each 0.5 mm thick

(http://www.newlightphotonics.com/vl/bibo-standardproducts.html); lens 19 flat-curved with antireflection coating at 805-815 nm, focal length 40 mm

(https://www.thorlabs.com/thorproduct.cfm?partnumber=LA1422-B); notch filter 20 at 405 nm (https://www.thorlabs.com/thorproduct.cfm7partnumberfNE405-13); beam splitter 21 (50:50) in the range 805-815 nm

(https://www.thorlabs.com/thorproduct.cfm?partnumber=BSW29); half-wave plates of zero order 22, 24, 26, 28, 59 with antireflection at a wavelength of 810 nm (https://www.thorlabs.com/thorproduct.cfm?partnumber=WPH10E-808); quarter-wave plates 23, 25, 27, 29 of the zero order with antireflection at a wavelength of 810 nm (https://www.thorlabs.com/thorproduct.cfm7partnumberfVPQ10E-808); polarizing beam splitting cubes 30, 31, 58, 61 for radiation in 805-815 nm range (https://www.thorlabs.com/thorproduct.cfm?partnumber=PBS202); single-mode polarization-storing fiber 32, 33, 34, 35, 63, 64 in the range 805-815 nm (https://www.thorlabs.com/thorproduct.cfm?partnumber=Pl-780PM-FC-2); silicon single-photon detectors 36, 37, 38, 39 for the range 805-815 nm (https://www.lasercomponents.com/de-en/product/count-nir/); interference filter 40, 41, 42 with a center wavelength of 810 nm and an FWHM of 10 nm

(https://www.thorlabs.com/thorproduct.cfm?partnumber=FB810-10); motorized translational slide 43 with a stroke of 25 mm (https://www.thorlabs.com/thorproduct.cfm?partnumber=PTl/M-Z8); single-mode fiber beam splitter 44 in the range 805-815 nm; correlator 45 for processing pulses coming from detectors 36-39, using "start-stop" schemes (https://www.picoquant.com/products/category/tcspc-and-time-tagging- modules / multiharp-150-high -throughput-multichannel-event-timer-tcspc- unit # specification); couplers 47-48 for 405 nm radiation, consisting of a tube with a fiber adapter at one end and a lens with a focal length of 10 mm, coated at 405 nm; couplers 49-57 for emission at 810 nm, consisting of a tube with a fiber adapter at one end and a lens with a focal length of 10 mm, coated at 810 nm; balanced detector 62 (https://www.thorlabs.com/thorproduct.cfm?partnumber=PDB450A); mirror with piezo-movable 65 with controller

(https://www.thorlabs.com/thorproduct.cfm?partnumber=KPZNFL5/M);

Thus, the developed educational and scientific laboratory stand provides the ability to solve all the above problems of quantum physics. The inventive stand can be used to teach university students, employees of educational institutions, scientific organizations and industrial companies the basics of implementing optical circuits used in quantum communications and quantum computing technologies.

Claims

CLAIM

1. Educational and scientific laboratory stand for researching the polarization and correlation properties of single-photon, biphoton, coherent and thermal light fields, Hong-Oy-Mandel interference, and homodyne detection, including a pump laser module connected in series by optical communication, a biphoton source module, polarization modules measurements in channels A and B, a correlation measurement module configured to be connected to a computer, as well as a coherent and thermal state source module and a homodyne detection module, where a coherent and thermal state source module is configured to be connected by optical communication or with polarization measurement modules in channels A and B, or with a homodyne detection module, and the homodyne detection module is designed to be connected to a computer, while the pump laser module contains a laser with a current and temperature controller, the biphoton source module contains in one optical path, a biphoton radiation polarization controller, nonlinear crystals, a system for separating biphoton radiation and pump radiation; channels A and B of the polarization measurement modules contain biphoton radiation polarization controllers, a polarization filter and / or a beam splitter; the correlation measurement module contains single-photon detectors connected to a pulse correlator configured to be connected to a computer; the module of the source of coherent and thermal states contains a laser connected by optical communication with a beam splitter made with the possibility of dividing light into two channels, in one of which there is a matt disk made with the possibility of rotation around its center to randomly modulate the laser radiation in phase and amplitude, both channels are made with the possibility of connecting to the polarization measurement modules and the homodyne detection module; the homodyne detection module contains the first polarization beam splitter, the inputs of which are made with the possibility of connecting to the outputs of the source of coherent and thermal states, and in its output channel there is a polarization controller, a second polarizing beam splitter, and optically coupled light detectors.

2. Educational and scientific laboratory stand according to claim 1, characterized in that the biphoton radiation polarization controller in the biphoton source module and polarization measurement modules consists of sequentially located half-wave and quarter-wave phase plates mounted on slides made with the possibility of rotation.

3. An educational and scientific laboratory stand according to claim 2, characterized in that the phase plates of the polarization controller in the biphoton source module are designed for the pump laser wavelength, and the phase plates of the polarization controllers in the polarization measurement modules are designed for twice the wavelength.

4. Educational and scientific laboratory stand according to claim 2, characterized by the fact that the biphoton radiation polarization controllers in the biphoton source module and polarization measurement modules are made on slides with the ability to rotate around the optical axis, while the slides are made with the ability to connect to a computer and automatically adjust the angle turning the slides.

5. Educational and scientific laboratory stand according to claim 1, characterized in that optical fiber is used as an optical connection connecting the modules.

6. Educational and scientific laboratory stand according to claim 1, characterized in that the laser in the pump laser module is a laser diode installed in a collimation tube, with the possibility of temperature stabilization by using a Peltier element connected to a current and temperature controller.

7. Educational and scientific laboratory stand according to claim 1, characterized in that the pump laser module contains a coupler - a device for input / output of radiation into an optical fiber, which is a tube with a lens, in the focal plane of which the end of the optical fiber is located for communication with an adjacent module.

8. Educational and scientific laboratory stand according to claim 7, characterized in that the pump laser module includes an optical isolator located between the laser and the coupler, preventing reflected radiation from entering the laser back into the laser.

9. Educational and scientific laboratory stand according to claim 7, characterized in that a pair of prisms is installed in the pump laser module between the laser and the coupler, which are made with the possibility of adjusting the beam shape for efficient introduction of radiation into the optical fiber.

10. Educational and scientific laboratory stand according to claim 6, characterized in that the laser diode in the pump laser module is configured to operate at a wavelength of 400-410 nm and has a line width of no more than 1 GHz.

11. Educational and scientific laboratory stand according to claim 6, characterized in that the laser diode contains a built-in high-Q resonator.

12. Educational and scientific laboratory stand according to claim 6, characterized by the fact that the pump laser module contains a diffraction grating connected to the laser diode by optical coupling to provide the required spectral width and performing the function of an external resonator mirror.

13. Educational and scientific laboratory stand according to claim 1, characterized in that the module of the source of biphotons from the entrance side contains a coupler, in the focal plane of the lens of which the end of the fiber is located for connection with the pumping module.

14. Educational and scientific laboratory stand according to claim 1, characterized in that the biphoton source module is configured to connect to polarization measurement modules in channels A and B using a coupler, in the focal plane of the lens of which the end of the fiber is located.

15. Educational and scientific laboratory stand according to claim 1, characterized in that the frequency filter in the biphotone source module is made for a wavelength of 405 nm with antireflection in the range of 400-410 nm.

16. Educational and scientific laboratory stand according to claim 1, characterized in that the nonlinear crystals in the biphoton source module are made for degenerate phase matching of type I for the pump wavelength, with orthogonally oriented optical axes.

17. Educational and scientific laboratory stand according to claim 1, characterized in that the biphoton source module contains a frequency pump filter and a lens installed after the frequency pump filter and in front of the nonlinear crystals so that the crystals are in its focus, while the lens is made with antireflection coating at the pump wavelength.

18. Educational and scientific laboratory stand according to claim 1, characterized in that the biphoton source module contains a lens installed on the side of the module exit after the nonlinear crystals so that the crystals are in its focus, while the lens is made with an antireflection coating at twice its length pump waves.

19. Educational and scientific laboratory stand according to claim 18, characterized in that the module of the biphoton source contains a frequency filter installed on the exit side of the lens located after the nonlinear crystals, and made with the possibility of transmitting the radiation of biphotons at a doubled pump wavelength, but not transmitting radiation at the pump wavelength.

20. Educational and scientific laboratory stand according to claim 1, characterized in that the laser module of the source of coherent and thermal states has a fiber output, its spectrum width does not exceed 1 MHz, and the center wavelength is equal to twice the pump laser wavelength.

21. Educational and scientific laboratory stand according to claim 1, characterized in that the laser of the module of the source of coherent and thermal states is connected to the beam splitter using an optical fiber.

22. Educational and scientific laboratory stand according to claim 1, characterized in that the matt disk of the source of coherent and thermal states is connected to the output of the beam splitter and to the output optical fiber by means of couplers.

23. Educational and scientific laboratory stand according to claim 1, characterized in that the matt disk of the source of coherent and thermal states module is made with the possibility of adjusting the rotation speed, including a complete stop.

24. Educational and scientific laboratory stand according to claim 1, characterized in that the connection of the module of the source of biphotons and the module of the source of coherent and thermal states to the modules of polarization measurements in channels A and B is implemented by means of a beam-splitting plate having two inputs, one of which is connected to with the output of the biphoton source module, and the second with the output of the source of coherent and thermal states by means of a coupler, the outputs of the beam splitting plate are optically connected to the inputs of the polarization measurement modules in channels A and B.

25. Educational and scientific laboratory stand according to claim 1, characterized in that the modules of polarization measurements in channels A and B are connected to the module of correlation measurements by optical fibers by means of couplers, in front of which Narrow-band frequency filters with a transmission range of 10-40 nm are installed, the center of the transmission range of which coincides with the doubled wavelength of the pump laser.

26. Educational and scientific laboratory stand according to claim 1, characterized in that one of the couplers of the polarization measurement module in channel A is installed on a translational slide made with the ability to change the distance between it and the polarization filter and / or beam splitter.

27. Educational and scientific laboratory stand according to claim 26, characterized in that the translational movement is made with the ability to connect to a computer.

28. Educational and scientific laboratory stand according to claim 1, characterized in that the correlation measurement module contains four single-photon detectors, the optical inputs of which are connected to the optical outputs of the polarization measurement modules, while two of the four detectors are connected to the outputs of channels A and B through a symmetric fiber optic beam splitter.

29. Educational and scientific laboratory stand according to claim 1, characterized in that the pulse correlator is configured to count the number of photocounts for each channel, as well as measure the number of coincidences of photocounts between any two channels and measure the histogram of the delay times between pulses traveling along any of two channels.

30. Educational and scientific laboratory stand according to claim 1, characterized in that the homodyne detection module is equipped on the input side with couplers for connection by means of optical fibers with the module of the source of coherent and thermal states.

31. Educational and scientific laboratory stand according to claim 1, characterized in that the polarization controller in the homodyne detection module is made in the form of a half-wave phase plate for twice the pump wavelength.

32. Educational and scientific laboratory stand according to claim 1, characterized in that the light detectors in the homodyne detection module are connected to an ADC unit capable of being connected to a computer.

33. Educational and scientific laboratory stand according to claim 1, characterized in that the light detectors in the homodyne detection module are made in the form of a single module including a differential photocurrent amplifier.

34. Educational and scientific laboratory stand according to claim 1, characterized in that before the first polarization beam splitter of the homodyne detection module, a mirror is installed on a precision piezo slider connected to a sawtooth signal source.

35. Educational and scientific laboratory stand according to claim 1, characterized in that a long-focus lens is installed in front of the second polarizing beam splitter of the homodyne detection module, and the detectors are located from the lens at its focal length.

36. Educational and scientific laboratory stand according to claim 1, characterized in that it contains a computer connected to the stand modules, made with the possibility of remote connection of another computer with the possibility of remote control of all stand modules.

37. Educational and scientific laboratory stand according to claim 1, characterized in that the connection of the modules by fiber-optic optical communication is realized by means of a coupler - a device for input / output of radiation into the optical fiber, which is a tube with a lens, in the focal plane of which the end of the fiber is located.