KR20220077007A - Apparatus and method for optical-microwave quantum entangled photon pair generation, and quantum radar using the same - Google Patents

Abstract

An optical-microwave entangled photon pair generator uses a nonlinear crystal to split photons of a laser into a first signal mode and an idler mode having a quantum entanglement state, and a light wave entanglement photon pair generator converts the first signal mode to a magnon mode and an optical-microwave converter that converts the magnon mode into a microwave second signal mode and emits the light, wherein the idler mode and the second signal mode form a photon-microwave quantum entangled photon pair.

Description

Photo-microwave quantum entangled photon pair generating device and method, and quantum radar using same

The present invention relates to an apparatus for generating an optical-microwave quantum entangled photon pair, a method for generating the same, and a quantum radar using the same, and more particularly, to an apparatus for generating an optical-microwave quantum entangled photon pair using yttrium iron garnet crystals, and It relates to a method and a quantum radar using the same.

Quantum entanglement is a state in which two or more particles have entanglement, a strong correlation that cannot be explained by classical physical theory. The most widely used quantum entanglement state in quantum optics is called a two-mode squeezed vacuum (TMSV) state, and is a state in which two photons have an entangled relationship.

It is known that the quantum entanglement state can be sensed with higher sensitivity than before using entanglement, which is a quantum correlation. In particular, technologies such as quantum radar are known to be able to detect low reflectivity objects better than conventional radars, and are attracting attention as being able to detect objects with stealth characteristics.

However, there is a problem in frequency selection in implementing this. Longer wavelengths such as microwaves are more suitable than optical frequencies for detecting distant objects. On the other hand, long-wavelength microwaves have too low energy at the photon level, so their generation and detection are technically difficult.

The technical problem to be solved by the present invention is to provide an apparatus for generating an optical-microwave entangled photon pair using a yttrium iron garnet (YIG) crystal, a method thereof, and a quantum radar using the same.

Although light-microwave conversion has been studied, the experimental implementation of photon-level conversion has only been conducted relatively recently. In addition, these experiments are experiments in which one photon is converted into microwaves, and the form of maintaining the entangled state while converting one of the entangled photon pairs into microwaves has not been studied.

An optical-microwave entangled photon pair generator according to an embodiment of the present invention divides photons of a laser into a first signal mode and an idler mode having a quantum entanglement state using a nonlinear crystal, and the first a light-to-microwave converter that converts a signal mode into a magnon mode, converts the magnon mode into a microwave second signal mode and emits light, wherein the idler mode and the second signal mode are light-microwave quantum entanglement photons form a pair

The light wave entanglement photon pair generator includes a pump laser emitting light by raising the energy layer of electrons, and the first signal mode polarized in a first direction and the light incident from the pump laser polarized in a second direction Spontaneous parametric downconversion decisions to split into idler modes may be included.

The optical-microwave converter may include a yttrium iron garnet crystal that quantizes the first signal mode into a spin wave to convert it into the magnon mode, and a microwave resonator that converts the magnon mode into the second signal mode. have.

The optical-microwave converter may further include a magnet for forming an external magnetic field inside the microwave resonator, and the yttrium iron garnet crystal may be fixed at a point in the microwave resonator where the external magnetic field distribution is maximized.

The photo-microwave entangled photon pair generation method according to another embodiment of the present invention comprises the steps of dividing photons of a laser into a first signal mode and an idler mode having a quantum entanglement state using a nonlinear crystal, and using a yttrium iron garnet crystal. converting a first signal mode to a magnon mode, and converting the magnon mode to a second signal mode that is microwave and emitting, wherein the idler mode and the second signal mode are optical-microwave quantum entanglement form a photon pair.

The light incident from the pump laser may be divided into the first signal mode polarized in a first direction and the idler mode polarized in a second direction by using a spontaneous parameter down-conversion crystal.

The first signal mode may be converted into the magnon mode by a spin wave of the yttrium iron garnet crystal.

The magnon mode may be generated by fixing the yttrium iron garnet crystal in a microwave resonator, aligning the magnetic field of the yttrium iron garnet crystal with an external magnetic field, and then scanning two-frequency coherent lasers having modified polarizations.

A quantum radar according to another embodiment of the present invention divides photons of a laser into a first signal mode and an idler mode having a quantum entanglement state using a nonlinear crystal, and converts the first signal mode into a magnon mode, A light-microwave entangled photon pair generating device that converts a magnon mode into a microwave second signal mode and radiates it toward a subject, and a device that preserves the idler mode and collects the second signal mode reflected by the subject to and a meter for sensing, wherein the idler mode and the second signal mode form an optical-microwave quantum entangled photon pair.

The photo-microwave entangled photon pair generating device includes a yttrium iron garnet crystal that quantizes the first signal mode into a spin wave to convert it into the magnon mode, and a microwave resonator that converts the magnon mode into the second signal mode may include

Photon conversion using yttrium iron garnet (YIG) crystals can perform photo-microwave conversion even at room temperature rather than cryogenic temperature, so it is more advantageous for practical use than conversion methods that require cryogenic temperatures.

In addition, photon conversion using yttrium iron garnet (YIG) crystals enables conversion of a wider bandwidth than other optical-microwave conversion devices. Therefore, photon conversion using yttrium iron garnet (YIG) crystals is suitable for devices such as quantum radars that detect objects at various frequencies.

1 is a block diagram illustrating an apparatus for generating an optical-microwave entangled photon pair according to an embodiment of the present invention.
2 is a block diagram illustrating a light wave entanglement photon pair generator according to an embodiment of the present invention.
3 is a block diagram illustrating an optical-microwave converter using a yttrium iron garnet (YIG) crystal according to an embodiment of the present invention.
4 is a graph showing a change in the microwave-light wave conversion frequency due to the interaction between the magnon mode, the Kittel mode, and the microwave resonator.
5 is a graph showing a result of a microwave-light conversion experiment according to an embodiment.
6 is an exemplary view illustrating an optical-microwave converter using a yttrium iron garnet (YIG) crystal.
7 is a block diagram illustrating a quantum radar using an optical-microwave entangled photon pair generating apparatus according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in several different forms and is not limited to the embodiments described herein.

In order to clearly explain the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

In addition, throughout the specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating an apparatus for generating an optical-microwave entangled photon pair according to an embodiment of the present invention.

Referring to FIG. 1 , an optical-microwave entangled photon pair generating device 1 includes an optical-microwave entangled photon pair generator 10 and an optical-microwave converter 20 .

The light wave entanglement photon pair generator 10 divides a photon of a laser into two photons using a nonlinear crystal. In this case, the positional mode of the two photons may be different, and one of the two photons is called a signal mode and the other is called an idler mode. In other words, the light wave entanglement photon pair generator 10 generates a first signal mode SGN1 and an idler mode IDL. The first signal mode SGN1 and the idler mode IDL have a quantum entanglement state. The first signal mode SGN1 and the idler mode IDL are optical waves having a quantum entanglement state.

The quantum entangled state is called a two-mode squeezed vacuum (TMSV) state, and is a state in which two photons have an entangled relationship. The dual-mode vacuum compression (TMSV) state may be expressed as in Equation (1).

는 각 모드의 평균 광자 수를 나타낸다. 이러한 광학적 이중 모드 진공 압축(TMSV) 상태는 자발매개변수하향 변환(spontaneous parametric down-conversion, SPDC)을 이용하여 구현될 수 있다. 자발매개변수하향 변환(SPDC)은 펌프(pump) 레이저의 광자가 에너지와 운동량을 보존하면서 두 개의 광자로 쪼개지는 현상을 나타낸다. 이때, 자발매개변수하향 변환(SPDC)의 과정에 따라 두 개의 광자인 시그널 모드와 아이들러 모드의 주파수를 다르게 하는 것이 가능하다.Here, S and I, which are the lower alphabets of the vector, mean photons of signal mode and idler mode, respectively.

represents the average number of photons in each mode. This optical dual-mode vacuum compression (TMSV) state can be implemented using spontaneous parametric down-conversion (SPDC). Spontaneous parameter downconversion (SPDC) refers to the phenomenon in which a photon of a pump laser is split into two photons while conserving energy and momentum. In this case, it is possible to make the frequencies of the signal mode and the idler mode, which are two photons, different according to the process of spontaneous parameter down-conversion (SPDC).

The light-to-microwave converter 20 converts a first signal mode SGN1 into a second signal mode SGN2 that is microwaves using a yttrium iron garnet (YIG) crystal and a microwave cavity. That is, the optical-microwave converter 20 converts light waves into microwaves.

The idler mode (IDL), which is a light wave, and the second signal mode (SGN2), which is a microwave, form a light-microwave quantum entangled photon pair. In this way, the optical-microwave entangled photon pair generating device 1 may generate the optical-microwave quantum entangled photon pair.

2 is a block diagram illustrating a light wave entanglement photon pair generator according to an embodiment of the present invention. The light wave entanglement photon pair generator 10 of FIG. 1 may be implemented as shown in FIG. 2 .

Referring to FIG. 2 , the light wave entanglement photon pair generator 10 may include a pump laser 110 and a spontaneous parameter down conversion (SPDC) crystal 120 .

The pump laser 110 is a laser device that increases the energy layer of electrons from a low energy state to a high energy state by absorbing light from a light source by electrons. Light emitted from the pump laser 110 is incident on the SPDC crystal 120 which is a non-linear crystal. Nonlinear crystals include beta barium borate (BBO) crystals.

The SPDC crystal 120 divides a photon of the light incident from the pump laser 110 into two photons probabilistically to form a first signal mode SGN1 and an idler mode IDL. The first signal mode SGN1 may be vertically polarized P polarization, and the idler mode IDL may be horizontally polarized S polarized light. A polarization direction of the first signal mode SGN1 may be orthogonal to a polarization direction of the idler mode IDL.

When a photon of frequency f and momentum k generated by the pump laser 110 enters the SPDC crystal 120 , the photon is probabilistically divided into two photons (a first signal mode SGN1 and an idler mode IDL). Spontaneous parameter downconversion (SPDC) occurs while satisfying the law of conservation of energy and conservation of momentum, so if the signal mode is S and the idler mode is I, the frequency and momentum of two photons satisfy the conditions of Equation 2.

The entangled photon pair generated through spontaneous parametric down-conversion (SPDC) has the dual-mode vacuum compression (TMSV) state mentioned in Equation 1.

Photons of the idler mode (IDL) are preserved without interaction with the outside, and photons of the first signal mode (SGN1) may be optically-microwave converted using the optical-microwave converter 20 .

3 is a block diagram illustrating an optical-microwave converter using a yttrium iron garnet (YIG) crystal according to an embodiment of the present invention. The optical-microwave converter 20 of FIG. 1 may be implemented as shown in FIG. 3 .

Referring to FIG. 3 , the optical-microwave converter 20 may include a mixed system 210 , and the mixed system 210 may include a yttrium iron garnet (YIG) crystal 211 and a microwave resonator 212 . . Optical-microwave conversion using the YIG crystal 211 is performed via the Kittel mode of the YIG crystal 211 and the mixed system 210 of the microwave resonator 212 .

When the first signal mode (SGN1) is incident on the YIG crystal 211, the first signal mode (SGN1) is converted to the kitel mode (KTTL) (magnon mode) by the YIG crystal 211, the microwave resonator 212 is entered into The YIG crystal 211 is a ferromagnetic material having a high spin density. Spin waves may exist in a ferromagnetic material, and these spin waves can be described as conservation following Bose statistics. A particle obtained by quantizing a spin wave is called a magnon, and among them, a spatially uniform magnetostatic mode is called a kitel mode (KTTL). The YIG crystal 211 may quantize the first signal mode SGN1 into a spin wave and convert it into a magnon mode (Kittel mode KTTL).

The microwave resonator 212 emits a second signal mode SGN2 that is a microwave by converting the kitel mode KTTL (magnon mode) into microwaves.

Light waves, microwaves in the microwave resonator 212, and Kittel modes can be physically expressed using a Hamiltonian as shown in Equation (3).

,

,

,

는 각각 마이크로파 공진기 모드, 내부 순환 마이크로파 모드, 광파 모드, 마그논 모드의 소멸 연산자를 나타낸다.

는 입출력 손실,

는 공진 주파수,

와

는 각각 마이크로파-마그논과 광자-마그논 연결(coupling) 효율을 나타낸다. 아래첨자 알파벳 o, e, m은 각각 광파, 마이크로파, 마그논에 대한 물리량을 나타낸다. 각 식은 첫 번째 식부터 전체 물리계, 내부 순환 마이크로파와 마이크로파 공진기 모드의 상호 작용계, 마이크로파 공진기 모드와 마그논 모드의 상호 작용계, 광파와 마그논 모드의 상호 작용계의 해밀토니안을 의미한다.From here

,

,

,

denotes the extinction operators of the microwave resonator mode, internal circulation microwave mode, light wave mode, and magnon mode, respectively.

is the input/output loss,

is the resonant frequency,

Wow

denotes microwave-magnon and photon-magnon coupling efficiency, respectively. The subscript alphabets o, e, and m represent physical quantities for light waves, microwaves, and magnons, respectively. Each equation means the Hamiltonian of the entire physical system from the first equation, the interaction system of internal circulation microwave and microwave resonator mode, the interaction system of microwave resonator mode and magnon mode, and the interaction system of light wave and magnon mode.

4 is a graph showing a change in the microwave-light wave conversion frequency due to the interaction between the magnon mode, the Kittel mode, and the microwave resonator.

Referring to FIG. 4 , the horizontal axis of the graph represents the external magnetic field, and the vertical axis represents the microwave frequency. The horizontal dotted line indicates the resonance frequency of the microwave resonator 212, and the diagonal dotted line indicates the frequency of the Kittel mode. The frequency of the Kittel mode (magnon mode) varies according to the external magnetic field, and this frequency approaches the resonance frequency of the microwave resonator 212, and the frequency of the Kittel mode and the resonance frequency of the microwave resonator 212 interact and mix It can be seen that the resonance frequency of the system 210 is changed.

The input/output relation of the microwave resonator 212 can be obtained using the quantum Langevin equation, which is the equation of motion of the Hamiltonian and open systems of the entire physical system. It can be expressed as Equations 4 and 5.

는 광학-마그논 모드의 연결 효율 평균과 마이크로파-마그논 모드의 연결 효율 평균, 그리고 마이크로파 주파수와 키텔 모드의 주파수 차이를 이용하여 구해지는 값이다. 수학식 4 및 5로부터 YIG 결정(211)과 마이크로파 공진기(212)의 혼합계(210)를 이용하여 광파의 광자가 마이크로파의 광자로 변환되고, 마이크로파의 광자가 광파의 광자로 서로 변환될 수 있고, 그 변환 효율은 서로 다른 입출력 연산자의 계수의 절대값 제곱으로 주어짐을 알 수 있으며, 광-마이크로파 변환과 마이크로파-광 변환의 효율이 같음을 확인할 수 있다.Here, the subscripts in and out mean a wave entering the microwave resonator 212 and a wave coming out, respectively.

is a value obtained using the average of the connection efficiency of the optical-magnon mode, the average of the connection efficiency of the microwave-magnon mode, and the difference between the microwave frequency and the frequency of the Kittel mode. From Equations 4 and 5, using the mixed system 210 of the YIG crystal 211 and the microwave resonator 212, photons of light waves are converted into photons of microwaves, and photons of microwaves can be converted into photons of light waves. , it can be seen that the conversion efficiency is given as the square of the absolute value of the coefficients of different input/output operators, and it can be confirmed that the optical-microwave conversion and the microwave-light conversion efficiency are the same.

5 is a graph showing a result of a microwave-light conversion experiment according to an embodiment.

Referring to FIG. 5 , data of a microwave-light conversion experiment are shown. It can be seen that a light intensity of 74 dBm is output after a microwave of 10 dB is input to the microwave resonator 212 . Considering the power loss in the cable and the gain of 30dB of the photodetector, it can be seen that the conversion efficiency is about 120dB or more. It can be seen that the background noise and the converted optical signal are clearly distinguished. As confirmed in Equations 4 and 5, it can be seen that the conversion efficiency of optical-microwave conversion will be about -120 dB or more to the same extent.

6 is an exemplary view illustrating an optical-microwave converter using a yttrium iron garnet (YIG) crystal.

Referring to FIG. 6 , the optical-microwave converter 20 may be implemented with a YIG crystal 211 , a microwave resonator 212 , and a magnet 213 .

The magnet 213 is mounted on the outside of the microwave resonator 212 and forms an external magnetic field inside the microwave resonator 212 .

The YIG crystal 211 is located inside the microwave resonator 212 . The YIG crystal 211 may be fixed at a point where the external magnetic field distribution is maximized in the microwave resonator 212 . The magnetic field of the YIG crystal 211 is aligned through the external magnetic field. Here, a magnon mode is generated by generating a precession of spin in the YIG crystal 211 using a two-frequency coherent laser having polarization perpendicular to each other. For light-microwave conversion, light of one frequency is continuously scanned from the pump laser 110, and when a single photon of another frequency is input, a magnon mode may be generated. The generated magnon mode is converted into microwaves through the microwave resonator 212 . At this time, in order to increase the efficiency, the frequency difference of the two-frequency coherent laser is the frequency of the microwave resonator 212 . An optical resonator may be added to improve the conversion efficiency.

As described above, the optical-microwave entangled photon pair generating device 1 may generate an optical-microwave quantum entangled photon pair.

Using a physical law that does not include quantum mechanics, the maximum value of the magnitude of the phase-sensitive correlation of two modes cannot exceed the square root of the product of the number of photons in each mode, which is expressed in Equation 6 can be expressed as

Here, the subscripts S and I indicate the signal mode and the idler mode, respectively. However, two modes in an entangled relationship, which are quantum correlations, may violate the above inequality. In the case of a dual-mode vacuum compression (TMSV) state, which is an entangled state, it may have values such as Equations 7 and 8.

That is, it can be confirmed that the two modes in the entangled relationship that are quantum correlations as in Equations 7 and 8 violate the inequality of Equation 6 . Therefore, in the case of such a Gaussian quantum state, an entanglement metric (EM) can be defined as in Equation 9.

If the entanglement metric (EM) value is greater than 1, then the quantum state is said to be entangled. In the case of the light-microwave entanglement state, the entanglement metric EM as in Equation 10 may be used by using the microwave extinction operator instead of the light wave extinction operator.

When there is no microwave input, the expected value to be used in Equation 10 can be calculated as Equation 11 by using the dual-mode vacuum compression (TMSV) state (Equation 1) and the optical-microwave input/output relational expression (Equation 4).

Thus, without taking into account the loss of the microwave resonator 212 and in the absence of a microwave input, it is found that, regardless of conversion efficiency, optical-microwaves have entanglement metric (EM) values such as dual-mode vacuum compression (TMSV) conditions. can be checked

Quantum information protocols that use quantum entanglement, such as quantum illumination and quantum ghost imaging, show quantum dominance by measuring phase-sensitive correlation values. Using the light-microwave entangled photon pair generating device 1 according to the embodiment of the present invention, the wavelength for detecting or imaging an object is a microwave to detect an object at a greater distance while preserving photons of the light wave to improve measurement accuracy It can be increased, and a more efficient quantum information protocol can be implemented.

7 is a block diagram illustrating a quantum radar using an optical-microwave entangled photon pair generating apparatus according to an embodiment of the present invention.

Referring to FIG. 7 , the quantum radar may include an optical-microwave entangled photon pair generating device 1 and a measuring device 2 .

The light-microwave entangled photon pair generating apparatus 1 may generate the idler mode IDL and the second signal mode SGN2 as described above. The idler mode (IDL) is transmitted to the measuring device (2) and preserved, and the second signal mode (SGN2) is radiated toward the subject (3). The second signal mode SGN2 is reflected by the subject 3 and is incident on the measuring device 2 .

The measuring device 2 may detect the position and shape of the subject 3 by combining the idler mode IDL and the second signal mode SGN2 reflected by the subject 3 . The measuring device 2 may generate an image of the subject 3 by combining the idler mode IDL and the second signal mode SGN2 . The measuring device 2 may be implemented in various structures capable of detecting the position, shape, etc. of the subject 3 by combining the idler mode (IDL) and the second signal mode (SGN2), and the structure of the measuring device 2 is not limited

The drawings and detailed description of the described invention referenced so far are merely exemplary of the present invention, which are only used for the purpose of explaining the present invention, and are used to limit the meaning or limit the scope of the present invention described in the claims. it is not Therefore, it will be understood by those of ordinary skill in the art that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims.

1: Light-microwave entangled photon pair generating device
10: Lightwave entanglement photon pair generator
20: optical to microwave converter
110: pump laser
120: SPDC decision
210: mixed system
211: Yttrium Iron Garnet (YIG) Crystal
212: microwave resonator
213: magnet

Claims (10)

a light wave entanglement photon pair generator that divides the photons of the laser into a first signal mode and an idler mode having a quantum entangled state using a nonlinear crystal; and
and an optical-microwave converter that converts the first signal mode into a magnon mode, converts the magnon mode into a microwave second signal mode and emits,
and the idler mode and the second signal mode form an optical-microwave quantum entangled photon pair. According to claim 1,
The light wave entangled photon pair generator,
a pump laser that emits light by raising the energy layer of electrons; and
and a spontaneous parameter down-conversion crystal dividing the light incident from the pump laser into the first signal mode polarized in a first direction and the idler mode polarized in a second direction. According to claim 1,
The optical-microwave converter,
a yttrium iron garnet crystal that quantizes the first signal mode into a spin wave and converts it into the magnon mode; and
and a microwave resonator for converting the magnon mode into the second signal mode. 4. The method of claim 3,
The optical-microwave converter,
Further comprising a magnet for forming an external magnetic field inside the microwave resonator,
The yttrium iron garnet crystal is fixed at a point where the external magnetic field distribution is maximized in the microwave resonator. splitting the photons of the laser into a first signal mode and an idler mode having a quantum entangled state using a nonlinear crystal;
converting the first signal mode to a magnon mode by using a yttrium iron garnet crystal; and
Converting the magnon mode to a microwave second signal mode and emitting it,
wherein the idler mode and the second signal mode form an optical-microwave quantum entangled photon pair. 6. The method of claim 5,
A method of generating light-microwave entangled photon pairs by dividing light incident from a pump laser into the first signal mode polarized in a first direction and the idler mode polarized in a second direction using a spontaneous parametric down-conversion crystal. 6. The method of claim 5,
A method of generating an optical-microwave entangled photon pair for converting the first signal mode into the magnon mode with a spin wave of the yttrium iron garnet crystal. 8. The method of claim 7,
Optical-microwave generating the magnon mode by fixing the yttrium iron garnet crystal in a microwave resonator, aligning the magnetic field of the yttrium iron garnet crystal with an external magnetic field, and then scanning a two-frequency coherent laser having modified polarizations A method of generating entangled photon pairs. By using a nonlinear crystal, the photons of the laser are divided into a first signal mode and an idler mode having a quantum entanglement state, the first signal mode is converted to a magnon mode, and the magnon mode is converted to a microwave second signal mode a light-to-microwave entangled photon pair generating device that radiates toward the subject; and
Preserving the idler mode, including a measuring device for detecting the subject by collecting the second signal mode reflected on the subject,
wherein the idler mode and the second signal mode form a photon-microwave quantum entangled photon pair. 10. The method of claim 9,
The light-microwave entangled photon pair generating device,
a yttrium iron garnet crystal that quantizes the first signal mode into a spin wave and converts it into the magnon mode; and
Quantum radar including a microwave resonator for converting the magnon mode into the second signal mode.

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