JP4030352B2 - Quantum correlation photon pair amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a quantum correlation photon pair amplification device. More specifically, the invention of this application relates to a quantum correlation photon pair amplification device capable of highly efficiently amplifying a quantum correlation photon pair generated from a parametric crystal where parametric fluorescence is generated and amplified.
[0002]
[Prior art and its problems]
In recent years, with the spread of the Internet, quantum cryptography communication systems, which are cryptographic systems using the principles of quantum mechanics, which are said to be more secure than conventional cryptosystems, have attracted attention. Quantum teleportation using the principle of quantum mechanics has attracted attention as well as systems, but quantum correlation photon pairs in a quantum correlation state are used in such quantum cryptography communication systems and quantum teleportation.
[0003]
As a method of generating a quantum correlation photon pair, a method using signal idler light (ω _s , ω _i ) generated simultaneously by performing parametric down conversion on incident excitation light (ω _p ) as shown below It has been known. The “parametric crystal” refers to a second-order nonlinear crystal that generates and amplifies parametric fluorescence.
[0004]
When excitation light (frequency ω _p , wave number K _p ) is incident on a parametric crystal where parametric fluorescence is generated and amplified, two photon pairs (energy is lower than the incident excitation light) due to the parametric down-conversion process in the parametric crystal ( Signals (ω _s , K _s ) and idlers (ω _i , K _i )) are generated simultaneously. These photon pairs are emitted from the parametric crystal at the same time, and are always generated so as to be correlated with frequency, wave number, and polarization (ω _p = ω _s + ω _i , K _p = K _s + K _i ; phase matching condition). Quantum correlated photon pairs generated in this way are widely used to study the generation of squeezed and entangled states, but the conventional method of generating quantum correlated photon pairs is very efficient in the down-conversion process using parametric crystals. Only small and very weak quantum correlation photon pairs can be obtained.
[0005]
Actually, entangled photon pairs are produced using such quantum correlated photon pairs, and experiments such as quantum teleportation have been conducted, but the generation efficiency of quantum correlated photon pairs as the light source is very low. In order to confirm the success of quantum teleportation, an enormous amount of experiment time of 10 hours to several days is required. Further, when considering application to processing technology, it is difficult to perform processing because the light density is too low, and a method for increasing the light density of the quantum correlation photon pair is strongly demanded.
[0006]
Although it is possible to amplify and oscillate two photon pairs (signal idler light) with respect to the pumping light using a conventional parametric amplifier, oscillator, etc., a linear resonator is generally adopted as the resonator structure. Each generated signal idler light is amplified through a separate optical path. Alternatively, only one of the signal idler light is amplified. For this reason, the conventional commercial apparatus does not consider simultaneously amplifying the signal light and the idler light.
[0007]
In the situation described above, several ideas have been proposed to amplify and use quantum correlated photon pairs at the same time. For example, in A. Lamas-Linares et al. (Published in Nature 412, 887 (2001)) 2, the excitation light pulse (40) is incident on the parametric crystal (41), and the generated quantum correlation photon pair (42A), (42B) travels in the same optical path in the opposite direction, and the mirror ( 43A) and (43B) to reflect the parametric crystal (41) again at the same time, and adjust the position of the excitation light folding mirror (44) in order to measure the timing of the excitation light pulse (40) folding, Increasing the number of quantum correlation photon pairs by re-injecting the folded excitation light pulse (40) and the quantum correlation photon pairs (42A) and (42B) that have traveled the optical path into the parametric crystal simultaneously. Successful in width. Note that the amplified photon pair includes another parametric crystal (45A) and (45B) and a polarization beam splitter (46A) and (46B) for correcting the optical path of the photon pair birefringed in the parametric crystal (40). And it passes through filters (47A), (47B), (47C), (47D) and is detected by avalanche photodiodes (48A), (48B), (48C), (48D). Reference numeral (49) denotes a half-wave plate.
[0008]
However, in the above method, since amplification is performed only by one pass, a quantum correlation photon pair having sufficient intensity has not been obtained.
[0009]
Therefore, the invention of this application has been made in view of the circumstances as described above, and can solve the problems of the prior art and amplify the quantum correlation photon pair generated from the parametric crystal with high efficiency. It is an object to provide a quantum correlation photon pair amplification device.
[0010]
[Means for Solving the Problems]
The invention of this application is to solve the above problems. First, parametric crystals for generating a quantum correlation photon pair and parametric fluorescence generation, parametric fluorescence amplification, excitation light folding mirror, quantum correlation photon are performed. Having a mirror for reflection, a modulator, and an optical delay circuit so that the optical path of the quantum correlation photon pair generated by the parametric crystal when the excitation light pumped by the laser is incident on the parametric crystal has an eight-character shape, Parametric crystal, excitation light folding mirror, quantum correlation photon pair reflection mirror, modulator and optical delay circuit are arranged, and the quantum correlation photon pair generated by the parametric crystal is fed back to the parametric crystal at the same time, and the excitation light folding mirror Quantum correlation advanced in the optical path by adjusting the position of The quantum correlation photon pair that has traveled the optical path can be obtained by causing the excitation light reflected by the optical pair and the excitation light folding mirror to simultaneously enter the parametric crystal and adjusting the optical path length of the quantum correlation photon pair by the optical delay circuit. Provided is a quantum correlation photon pair amplification device characterized in that another new excitation light is simultaneously incident on a parametric crystal .
[0011]
Second, the invention of this application provides the quantum correlation photon pair amplification device according to the first invention, wherein the excitation light is an excitation light pulse.
[0012]
Thirdly, in the first or second invention, the quantum correlation photon pair amplification is characterized in that the quantum correlation photon pair is taken out from the modulator by synchronizing the modulator and the generated quantum correlation photon pair. Providing equipment.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The quantum correlation photon pair amplification device of the invention of this application is a parametric crystal (nonlinear crystal) in which parametric fluorescence generation and parametric fluorescence amplification for quantum correlation photon pair generation are performed, an excitation light folding mirror, and a quantum correlation photon pair reflection mirror. A parametric crystal having a modulator and an optical delay circuit, so that the optical path of the quantum correlation photon pair generated by the parametric crystal when the laser-excited excitation light is incident on the parametric crystal, It has a resonator structure in which an excitation light folding mirror, a quantum correlation photon pair reflection mirror, a modulator, and an optical delay circuit are arranged. Note that the parametric crystal, the quantum correlation photon pair reflection mirror, and the like are arranged so that two 8-shaped annular optical paths have the same size, that is, are symmetric with respect to the parametric crystal.
[0016]
As the excitation light, an excitation light pulse oscillated from a pulse laser or the like can be used. At this time, since the conversion efficiency of the parametric crystal into parametric fluorescence is very low, a high-intensity laser is required. Moreover, since it is necessary to satisfy the phase matching condition at the same time, the flash lamp and the excitation by current injection that are used for normal laser excitation cannot be used.
[0017]
Since the quantum correlation photon pair amplification device of the invention of this application has the above-described structure, the quantum correlation photon pair generated from the parametric crystal passes through the same optical path in the opposite direction and is fed back to the parametric crystal at the same time. As a result, it is possible to amplify the quantum correlation photon pair generated simultaneously without destroying the quantum correlation, and to obtain the quantum correlation photon pair with high efficiency.
[0018]
In addition, the quantum correlation photon pair amplification device of the invention of this application can adjust the optical path length of the excitation light that has passed through the parametric crystal by adjusting the position of the excitation light folding mirror. Quantum correlation photon pairs generated by the folded excitation light and the parametric crystal and proceeding in the optical path can be simultaneously incident on the parametric crystal, so that the fed back quantum correlation photon pairs simultaneously induce stimulated emission and maintain quantum correlation. It is possible to amplify the quantum correlation photon pair as it is.
[0019]
In addition, by adjusting the optical path length of the quantum correlation photon pair with an optical delay circuit inserted in the middle of the optical path of the quantum correlation photon pair, the quantum correlation photon pair that has traveled along the optical path and another new excitation light are simultaneously converted into a parametric crystal. It can be made incident.
[0020]
Further, in the quantum correlation photon pair amplification device, the quantum correlation photon pair can be taken out from the modulator at a certain timing by synchronizing the modulator and the generated quantum correlation photon pair. At this time, for example, the advanced distances of the quantum correlation photon pairs are equal, as in the position of the midpoint between the two quantum correlation photon pairs reflecting mirrors that are first reflected by the parametric crystal. The modulator is placed at a symmetrical position.
[0021]
By the way, the state of a quantum correlation photon pair is very easy to destroy. For example, when one photon of a photon pair in a quantum correlation state is absorbed, the quantum correlation disappears at that time. Especially in the resonator, even slight losses such as absorption and scattering are greatly amplified. For example, when considering the case where a photon goes back and forth in a resonator with a transmittance of 99%, the probability that the photon will go back and forth 1000 times is 0.99 ^{1000 to} 0%. In other words, even in the resonator, even a very small loss destroys the quantum correlation photon pair. Therefore, it is important to avoid loss by paying close attention to the reflectivity of the components constituting the resonator, for example, the reflectivity of the mirror and the transmittance of the lens, crystal, modulator, and the like.
[0022]
Next, a specific configuration of the quantum correlation photon pair amplification device of the invention of this application will be described.
[0023]
For example, as shown in FIG. 1, in the quantum correlation photon pair amplification device (1), the quantum correlation is caused by the parametric crystal (3) excited by the excitation light pulse (frequency 2ω) (2) oscillated from the pulse laser. Photon pairs (frequency ω) (4A) and (4B) are generated. The generated quantum correlation photon pairs (4A) and (4B) are emitted to the optical paths a and b satisfying the phase matching condition, and the four quantum correlation photon pair reflection mirrors (5A), (5B), (5C), and (5D) It is made into an 8-character type by reflecting by. It should be noted that the parametric crystal (3), the quantum correlation photon pair reflection mirrors (5A), (5B), (5C), (5D), etc. so that the two annular optical paths of the eight-shape are symmetrical with respect to the parametric crystal. Is arranged.
[0024]
At this time, the modulator (6) is in an OFF state and does not act on the emitted quantum correlation photon pairs (4A) and (4B). Since the quantum correlation photon pairs (4A) and (4B) pass through the same optical path in the opposite direction, they enter the parametric crystal (3) again at the same timing. Further, the excitation light pulse (2) that has once passed through the parametric crystal (3) is folded by the excitation light pulse folding mirror (7). The pumping light pulse folding (2) folded by the pumping light pulse folding mirror (7) is incident on the parametric crystal (3) simultaneously with the quantum correlation photon pair (4A) and (4B). The position (M1) of the mirror (7) for use is adjusted.
[0025]
As a result, the re-incident quantum correlation photon pair (4A), (4B) and the pumping light pulse (2) folded back by the pumping light pulse folding mirror (7) are simultaneously amplified and then emitted to the optical paths c and d. The The optical paths c and d are the same as the optical paths a and b except that there is no modulator (6). The quantum correlation photon pairs (4A) and (4B) fed back in the opposite directions in the same optical path by the optical paths c and d reenter the parametric crystal (3) and are further amplified.
[0026]
At this time, an optical delay circuit in which the optical path lengths of the quantum correlation photon pairs (4A) and (4B) are inserted in the middle of the optical path so as to enter the parametric crystal (3) simultaneously with the second incident excitation light pulse (2) ( Adjust in step 8). When the amplified quantum correlation photon pair (4A) and (4B) are taken out at a certain timing, the modulator (6) is adjusted in accordance with the timing at which the quantum correlation photon pair (4A) and (4B) pass through the modulator (6). The quantum correlation photon pair (4A) and (4B) can be taken out to the outside by turning them on. By doing so, the quantum correlation photon pairs (4A) and (4B) can be amplified and extracted with high efficiency.
[0027]
As an application of the quantum correlation photon pair amplification device of the invention of this application, it contributes to the dramatic development of quantum information processing technology that has so far only been conducted verification experiments using very weakly entangled photon pairs. Can be expected. For example, the entangled quantum correlation photon pair can be easily produced by making the output quantum correlation photon pair beam incident and interfere from two surfaces of a non-polarizing beam splitter (50% reflectance). Since the quantum correlation photon pair used for fabrication is high in intensity, the entangled quantum correlation photon pair obtained can be expected to be much more efficient than the conventional method.
[0028]
In addition, it is considered to be used as a basic technology that is indispensable in the actual application of these information processing technologies. Furthermore, it can be applied to nano-processing technology using quantum effects, and nano-processing experiments that far exceed the diffraction limit of the processing laser light source used can be expected.
[0029]
Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail.
[0030]
【Example】
Using the quantum correlation photon pair amplification device (1) of the invention of this application shown in FIG. 1, the amplification factor of the photon pair of this quantum correlation photon pair amplification device (1) was measured.
[0031]
In the quantum correlation photon pair amplification device (1), the quantum correlation photon pair (frequency ω) (4A), (4B) is generated by the parametric crystal (3) excited by the excitation light pulse (frequency 2ω) (2). I let you. The generated quantum correlation photon pairs (4A) and (4B) are emitted to the optical paths a and b satisfying the phase matching condition, and the four quantum correlation photon pair reflection mirrors (5A), (5B), (5C), and (5D) It is made into an 8-character type by reflecting by. First, the quantum correlation photon pairs (4A) and (4B) travel along the optical paths a and b (reverse direction of the same optical path), respectively, and the quantum correlation photon pairs (4A) and (4B) and the excitation light pulse folding mirror (7). The folded excitation light pulse (2) is simultaneously incident on the parametric crystal (3), amplified, and then emitted to the optical paths c and d, and fed back in the same optical path by the optical paths c and d (4A ) And (4B) were incident again on the parametric crystal (3) and further amplified. At this time, the optical delay circuit (8) inserted in the middle of the optical path of the quantum correlation photon pair (4A) and (4B) so as to enter the parametric crystal (3) simultaneously with the second incident excitation light pulse (2). Their optical path lengths were adjusted. Then, according to the timing when the quantum correlation photon pair (4A), (4B) passes through the modulator (6), the modulator (6) is turned on, and the quantum correlation photon pair (4A), (4B) is extracted to the outside. It was.
[0032]
As a result of using the above-described apparatus, it has become possible to obtain a quantum correlation photon pair with higher efficiency than a conventional quantum correlation photon pair amplification apparatus.
[0033]
【The invention's effect】
As described in detail above, the invention of this application provides a quantum correlation photon pair amplification device that amplifies a quantum correlation photon pair with high efficiency.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram illustrating a quantum correlation photon pair amplification device according to the present invention.
FIG. 2 is a conceptual diagram illustrating a conventional quantum correlation photon pair amplification device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Quantum correlation photon pair amplification apparatus 2 Excitation light pulse 3 Parametric crystal 4 Quantum correlation photon pair pulse 5 Quantum correlation photon pair reflection mirror 6 Modulator 7 Excitation light folding mirror 8 Optical delay circuit

Claims (3)

A parametric crystal that generates parametric fluorescence and generates parametric fluorescence for generating a quantum correlation photon pair, a mirror for excitation light folding, a mirror for quantum correlation photon pair reflection, a modulator, and an optical delay circuit are laser-excited to the parametric crystal. Parametric crystal, excitation light folding mirror, quantum correlation photon pair reflection mirror, modulator, and optical so that the optical path of the quantum correlation photon pair generated by the parametric crystal when incident excitation light is incident becomes an 8-character type. A delay circuit is arranged, and the quantum correlation photon pair generated by the parametric crystal is fed back to the parametric crystal at the same time, and the position of the excitation light folding mirror is adjusted so that the quantum correlation photon pair that has traveled the optical path and the excitation light folding Simultaneously paramete the excitation light reflected by the mirror Tsu is incident to click crystal and quantum correlated photon pair by optical delay circuit by adjusting the optical path length, that is incident advanced optical paths of different quantum correlated photon pair to a new excitation light simultaneously parametrically crystal Characteristic quantum correlation photon pair amplification device.   2. The quantum correlation photon pair amplification device according to claim 1, wherein the excitation light is an excitation light pulse. 3. The quantum correlation photon pair amplification device according to claim 1, wherein the quantum correlation photon pair is taken out from the modulator by synchronizing the generated quantum correlation photon pair with the modulator .

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