A solid-state quantum storage device based on optical fiber microcavity

Abstract

The present invention provides a solid-state quantum storage device based on an optical fiber microcavity, relating to the field of quantum information technology. The device comprises: a light generating unit that generates pump light, reference light, and signal light; a rare earth ion-doped crystal film disposed within the optical fiber microcavity to store the signal light; the pump light, based on an atomic frequency comb scheme, generates specific absorption bands on the rare earth ion-doped crystal film corresponding to the parameters of the pump light, thereby adjusting the storage time of the signal light; and a regulating system that applies stress to the rare earth ion-doped crystal film, which, based on the piezoelectric spectroscopy effect, changes the light absorption frequency so that the center frequency of the light absorption frequency coincides with the frequency of the signal light. Furthermore, the cavity length of the optical fiber microcavity is adjusted to a cavity length corresponding to the frequency of the reference light, locking the cavity length of the optical fiber microcavity to achieve resonance of the signal light within the optical fiber microcavity and isolating the effects of vibration on the cavity length of the optical fiber microcavity. This invention achieves high-efficiency quantum storage of signal light of different frequencies.

Description

Technical Field

[0001] The present invention relates to the field of quantum information technology, and more particularly to a solid-state quantum storage device based on an optical fiber microcavity. Background Art

[0002] The quantum no-cloning theorem provides a fundamental guarantee for the security of quantum communication. However, this principle also limits the direct amplification of quantum signals, unlike classical signals. During optical fiber transmission, photons experience exponential attenuation losses with increasing distance, significantly hindering the possibility of achieving long-distance quantum communication over hundreds of kilometers using optical fiber channels. To overcome this challenge, three quantum memory-based solutions have been proposed: fiber quantum relays, portable quantum memory, and satellite-based free-space quantum communication. All of these solutions require the support of high-performance quantum memory.

[0003] Among numerous physical systems, rare-earth ion-doped crystals are widely used in quantum information technology due to their exceptional coherence times and energy-level lifetimes at liquid helium temperatures. The broadband nature of these crystals facilitates multimode multiplexing, which is crucial for increasing communication speeds and accelerating the practical application of quantum networks. Furthermore, as solid-state systems, rare-earth ion-doped crystals offer a significant advantage in their ease of processing and integration using existing, mature technologies.

[0004] However, most rare earth ion-doped crystals typically exhibit low optical transition strength, which means that their ability to absorb photons is relatively weak, resulting in low storage efficiency. Summary of the Invention

[0005] In view of this, the present invention provides a solid-state quantum storage device based on an optical fiber microcavity.

[0006] One aspect of the present invention provides a solid-state quantum storage device based on an optical fiber microcavity, comprising: a light generating unit and a microcavity storage unit; the light generating unit is used to generate pump light, reference light and signal light, and transmit the pump light, the reference light and the signal light to the microcavity storage unit; wherein the signal light carries quantum bit information to be stored; the microcavity storage unit is used to realize quantum storage of signal light of different frequencies; the microcavity storage unit comprises an optical fiber microcavity, a rare earth ion doped crystal film and an adjustment system; the rare earth ion doped crystal film is arranged inside the optical fiber microcavity; the rare earth ion doped crystal film is used to store the signal light; the pump light is based on An atomic frequency comb scheme generates specific absorption bands corresponding to the parameters of the pump light on the rare-earth ion-doped crystal film to adjust the storage time of the signal light. The adjustment system is used to apply stress to the rare-earth ion-doped crystal film to change the light absorption frequency of the rare-earth ion-doped crystal film based on the piezoelectric spectroscopy effect, so that the center frequency of the light absorption frequency is consistent with the frequency of the signal light. The adjustment system is also used to adjust the cavity length of the fiber microcavity to a cavity length corresponding to the frequency of the reference light based on the frequency of the reference light, thereby locking the cavity length of the fiber microcavity, achieving resonance of the signal light in the fiber microcavity, and isolating the influence of vibration on the cavity length of the fiber microcavity.

[0007] According to an embodiment of the present invention, the fiber microcavity includes a fiber concave mirror and a plane mirror; the fiber concave mirror and the plane mirror constitute an open Fabry-Perot cavity.

[0008] According to an embodiment of the present invention, the rare earth ion-doped crystal film includes an inner surface and an outer surface; the inner surface is the side facing the optical fiber concave mirror; the outer surface is the side opposite to the inner surface; the plane mirror is obtained by coating an optical anti-reflection film on the outer surface of the rare earth ion-doped crystal film.

[0009] According to an embodiment of the present invention, the adjustment system includes a cavity length locking system and a spring damping platform. The cavity length locking system is used to adjust the cavity length of the fiber microcavity to a cavity length corresponding to the frequency of the reference light according to the frequency of the reference light, thereby locking the cavity length of the fiber microcavity and actively isolating the effect of vibration on the cavity length of the fiber microcavity and achieving resonance of the signal light within the fiber microcavity. The spring damping platform is used to passively isolate the effect of vibration on the cavity length of the fiber microcavity.

[0010] According to an embodiment of the present invention, the above-mentioned adjustment system also includes a thin film stress adjustment device; the above-mentioned thin film stress adjustment device is arranged on the outer surface or inner surface of the above-mentioned rare earth ion-doped crystal film; the above-mentioned thin film stress adjustment device is used to apply stress to the above-mentioned rare earth ion-doped crystal film, based on the piezoelectric spectroscopy effect, change the light absorption frequency of the above-mentioned rare earth ion-doped crystal film, and make the center frequency of the above-mentioned light absorption frequency consistent with the frequency of the above-mentioned signal light.

[0011] According to an embodiment of the present invention, the above-mentioned device also includes a detection unit; the above-mentioned detection unit is used to receive the stored signal light output from the above-mentioned microcavity storage unit, count the cumulative number of the above-mentioned stored signal light over a period of time, and extract the quantum bit information in the above-mentioned stored signal light.

[0012] According to an embodiment of the present invention, the light generating unit includes a first laser, a second laser, an acousto-optic modulator, a signal light source, and a feedback optimization system; the first laser is used to generate the reference light; the second laser is used to generate the initial laser; the signal light source is used to generate signal light; the acousto-optic modulator is used to modulate the initial laser to obtain the pump light; and the feedback optimization system is used to adjust the parameters of the pump light based on the principle of atomic frequency comb dephasing and the cumulative amount of the stored signal light determined by the detection unit within the period of time.

[0013] According to an embodiment of the present invention, the above-mentioned detection unit includes a chopping device, a filtering device, a projection-based measurement device and a single-photon counting and time correlation device; the above-mentioned chopping device is used to remove the above-mentioned pump light from the optical signal output from the above-mentioned microcavity storage unit to obtain a detection optical signal; the above-mentioned filtering device is used to filter out the reference light in the above-mentioned detection optical signal to obtain the above-mentioned stored signal light; the above-mentioned projection-based measurement device is used to extract quantum bit information from the above-mentioned stored signal light; the above-mentioned single-photon counting and time correlation device is used to perform single-photon detection on the signal light after the quantum bit information is extracted, and to count the cumulative number of the signal light after the quantum bit information is extracted within the above-mentioned period of time.

[0014] According to an embodiment of the present invention, the cavity length of the above-mentioned fiber microcavity is set to range from 0.1 micron to 900 microns to increase the cavity resonance linewidth; the increased cavity resonance linewidth improves the storage bandwidth of the above-mentioned solid-state quantum storage device based on the fiber microcavity, thereby realizing temporal multi-mode multiplexing.

[0015] According to an embodiment of the present invention, the thickness of the rare earth ion doped crystal film is set to range from 0.1 micrometers to 900 micrometers, so that the stress of the rare earth ion doped crystal film is evenly distributed under the action of the film stress adjustment device.

[0016] According to an embodiment of the present invention, pump light is used to generate a specific absorption band corresponding to the parameters of the pump light on a rare earth ion-doped crystal film according to an atomic frequency comb scheme, thereby adjusting the storage time of the signal light. Stress is applied to the rare earth ion-doped crystal film by an adjustment system, and the light absorption frequency of the rare earth ion-doped crystal film is changed based on the piezoelectric spectroscopy effect, so that the center frequency of the light absorption frequency is consistent with the frequency of the signal light, thereby improving the absorption efficiency of the signal light in the specific absorption band. According to the frequency of the reference light, the cavity length of the fiber microcavity is adjusted to the cavity length corresponding to the frequency of the reference light, so that the cavity length of the fiber microcavity is locked to achieve resonance of the signal light in the fiber microcavity and isolate the influence of the vibration on the cavity length of the fiber microcavity, thereby achieving a relatively high energy transfer efficiency of the signal light and further improving the absorption efficiency of the signal light in the specific absorption band. Since the signal light carries the quantum bit information to be stored, the absorption efficiency of the signal light in the specific absorption band is improved, thereby improving the efficiency of quantum storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0018] Figure 1 A structural block diagram of a solid-state quantum storage device based on an optical fiber microcavity according to an embodiment of the present invention is shown.

[0019] Figure 2 A structural block diagram of a solid-state quantum storage device based on an optical fiber microcavity according to another embodiment of the present invention is shown.

[0020] Figure 3 FIG2 shows a schematic diagram of component connections of a solid-state quantum storage device based on an optical fiber microcavity according to another embodiment of the present invention.

[0021] Figure 4 A timing diagram of the storage process of a solid-state quantum storage device based on an optical fiber microcavity according to another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0023] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0024] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0025] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0026] In the embodiments of the present invention, the collection, updating, analysis, processing, use, transmission, provision, disclosure, and storage of all data involved (including, but not limited to, user personal information) comply with relevant laws and regulations, are used for legitimate purposes, and do not violate public order and good morals. In particular, necessary measures are taken to prevent unauthorized access to user personal information data and maintain the security of user personal information and network security.

[0027] In the embodiment of the present invention, the user's authorization or consent is obtained before obtaining or collecting the user's personal information.

[0028] Most rare earth ion-doped crystals typically exhibit low optical transition strengths, meaning they have relatively weak absorption of photons, resulting in low storage efficiency. High-efficiency quantum storage is crucial for the practical application of most quantum networks. To address this issue, researchers proposed using an impedance-matched Fabry-Perot cavity to enhance the interaction between light and matter. By implementing a cavity-enhanced atomic frequency comb scheme, they could theoretically achieve 100% storage efficiency.

[0029] The currently widely adopted approach is to combine millimeter-scale or larger Fabry-Perot cavities with bulk rare-earth ion-doped crystals. However, these designs have numerous drawbacks: On the one hand, the larger cavity length limits the cavity's resonant linewidth, and thus the memory's bandwidth; on the other hand, long cavities are often accompanied by large insertion loss and poor stability, further limiting the memory's efficiency. Furthermore, large cavity designs do not meet the practical application requirements of miniaturization and integration.

[0030] An embodiment of the present invention provides a solid-state quantum storage device based on an optical fiber microcavity.

[0031] Figure 1 A structural block diagram of a solid-state quantum storage device based on an optical fiber microcavity according to an embodiment of the present invention is shown.

[0032] like Figure 1 As shown, a solid-state quantum storage device based on an optical fiber microcavity includes: a light generating unit 11 and a microcavity storage unit 12; the light generating unit 11 is used to generate pump light, reference light and signal light, and transmit the pump light, reference light and signal light to the microcavity storage unit 12; wherein the signal light carries the quantum bit information to be stored; the microcavity storage unit 12 is used to realize quantum storage of signal light of different frequencies; the microcavity storage unit 12 includes an optical fiber microcavity 121, a rare earth ion doped crystal film 122 and an adjustment system 123; the rare earth ion doped crystal film 122 is arranged inside the optical fiber microcavity 121; the rare earth ion doped crystal film 122 is used to store signal light; the pump light is based on The atomic frequency comb scheme generates specific absorption bands corresponding to the parameters of the pump light on the rare earth ion-doped crystal film 122, thereby adjusting the storage time of the signal light. The adjustment system 123 is used to apply stress to the rare earth ion-doped crystal film 122, and based on the piezoelectric spectroscopy effect, changes the light absorption frequency of the rare earth ion-doped crystal film 122, so that the center frequency of the light absorption frequency is consistent with the frequency of the signal light. It is also used to adjust the cavity length of the fiber microcavity 121 to the cavity length corresponding to the frequency of the reference light according to the frequency of the reference light, so that the cavity length of the fiber microcavity 121 is locked, so as to achieve resonance of the signal light in the fiber microcavity 121 and isolate the influence of vibration on the cavity length of the fiber microcavity 121.

[0033] exist Figure 1 In the figure, the dotted arrows indicate that the regulating system 123 has a regulating effect on the optical fiber microcavity 121 and the rare earth ion-doped crystal film 122. For example, the dotted arrows between the regulating system 123 and the rare earth ion-doped crystal film 122 indicate that the regulating system 123 applies stress to the rare earth ion-doped crystal film 122. The dotted arrows between the regulating system 123 and the optical fiber microcavity 121 indicate that the regulating system 123 adjusts the cavity length of the optical fiber microcavity 121 and isolates the influence of vibration on the cavity length of the optical fiber microcavity 121.

[0034] According to an embodiment of the present invention, a microcavity storage unit utilizes a specific cavity-enhanced optical quantum storage scheme. This scheme uses pump light to create a specific absorption band in a rare-earth ion-doped crystal film. Reference light is used to adjust and lock the cavity length of the fiber microcavity. The piezoelectric spectroscopy effect is used to alter the optical absorption frequency of the rare-earth ion-doped crystal film, achieving high-efficiency quantum storage of signal light and frequency-tunable quantum storage. The specific cavity-enhanced optical quantum storage scheme is preferably a cavity-enhanced atomic frequency comb scheme. The signal light is a single-photon pulse.

[0035] According to an embodiment of the present invention, the adjustment system includes a cavity length locking system and a spring shock-absorbing platform; the cavity length locking system is used to adjust the cavity length of the optical fiber microcavity to a cavity length corresponding to the frequency of the reference light according to the frequency of the reference light, thereby locking the cavity length of the optical fiber microcavity and actively isolating the influence of vibration on the cavity length of the optical fiber microcavity and achieving resonance of the signal light in the optical fiber microcavity; the spring shock-absorbing platform is used to passively isolate the influence of vibration on the cavity length of the optical fiber microcavity. The spring shock-absorbing platform can utilize the physical properties of the spring to adaptively adjust the influence of vibration on the cavity length of the optical fiber microcavity.

[0036] According to an embodiment of the present invention, the adjustment system also includes a thin film stress adjustment device; the thin film stress adjustment device is arranged on the outer surface or inner surface of the rare earth ion doped crystal film; the thin film stress adjustment device is used to apply stress to the rare earth ion doped crystal film, based on the piezoelectric spectroscopy effect, change the light absorption frequency of the rare earth ion doped crystal film, and make the center frequency of the light absorption frequency consistent with the frequency of the signal light.

[0037] The rare earth ion-doped crystal film absorbs signal light based on a specific absorption band created by pump light and releases the signal light after a specified time. A spring damping platform is used to isolate the effects of vibration on the fiber microcavity's cavity length. A thin film stress adjustment device, based on the piezoelectric spectroscopy effect, modulates the light absorption frequency of the rare earth ion-doped crystal film by adjusting the stress applied to the thin film. The thin film stress adjustment device is provided with a channel for an optical path, which can be a reference light path, a pump light path, and / or a signal light path. The reference light path, the pump light path, and / or the signal light path pass through the thin film stress adjustment device. For example, the thin film stress adjustment device is provided with corresponding through-holes for the optical path. The spring damping platform and the cavity length locking system stabilize the cavity length of the open fiber microcavity through passive and active means, respectively. The spring damping platform is preferably a beryllium copper spring, whose spring stiffness is maintained well even at low temperatures. The specified time is determined by the specific absorption band created by the pump light.

[0038] According to an embodiment of the present invention, pump light is applied to a rare earth ion-doped crystal film according to an atomic frequency comb scheme to generate a specific absorption band corresponding to the parameters of the pump light, thereby adjusting the storage time of the signal light. Stress is applied to the rare earth ion-doped crystal film by an adjustment system, and the light absorption frequency of the rare earth ion-doped crystal film is changed based on the piezoelectric spectroscopy effect, so that the center frequency of the light absorption frequency is consistent with the frequency of the signal light, thereby improving the absorption efficiency of the signal light in the specific absorption band. The cavity length of the fiber microcavity is adjusted to a cavity length corresponding to the frequency of the reference light according to the frequency of the reference light, thereby locking the cavity length of the fiber microcavity to achieve resonance of the signal light in the fiber microcavity and isolating the influence of the vibration on the cavity length of the fiber microcavity, thereby achieving a relatively high energy transfer efficiency of the signal light and further improving the absorption efficiency of the signal light in the specific absorption band. Since the signal light carries the quantum bit information to be stored, by improving the absorption efficiency of the signal light in the specific absorption band, the efficiency of quantum storage is improved, and a high-efficiency, multi-mode, easily integrated, and frequency-tunable quantum storage function is achieved, which can be widely used in fields such as quantum communication and quantum computing.

[0039] According to an embodiment of the present invention, a fiber microcavity includes a fiber concave mirror and a plane mirror; the fiber concave mirror and the plane mirror constitute an open Fabry-Perot cavity, which is used to realize the function of adjustable cavity length and realize high-efficiency quantum storage of signal light based on the principle of cavity-enhanced interaction between light and matter.

[0040] According to an embodiment of the present invention, the fiber microcavity is an open Fabry-Perot cavity composed of a microscopic fiber concave mirror and a macroscopic plane mirror, and is used to enhance the interaction between signal light and rare earth ion-doped crystal films.

[0041] According to an embodiment of the present invention, the rare earth ion-doped crystal film includes an inner surface and an outer surface; the inner surface is the side facing the optical fiber concave mirror; the outer surface is the side opposite the inner surface; the plane mirror is obtained by coating the outer surface of the rare earth ion-doped crystal film with an optical anti-reflection coating, which is used to further improve the quantum storage efficiency of the signal light based on the principle of reducing intracavity loss. Specifically, the plane mirror of the optical fiber microcavity can be formed by coating the surface of the rare earth ion-doped crystal film away from the optical fiber concave mirror with a distributed Bragg reflector type anti-reflection coating. The optical fiber concave mirror is obtained by using carbon dioxide laser etching technology to produce the optical fiber concave surface on the optical fiber end face, and then using ion beam sputtering technology to coat the optical anti-reflection coating on the optical fiber concave surface.

[0042] According to an embodiment of the present invention, by coating an optical anti-reflection film on the outer surface of a rare earth ion-doped crystal film, the insertion loss of the rare earth ion-doped crystal film can be reduced, which is conducive to achieving high-efficiency quantum storage of signal light.

[0043] According to an embodiment of the present invention, a multimode optical fiber with a diameter of 125 μm can be used as the optical fiber, and the concave surface of the optical fiber can be prepared by carbon dioxide laser ablation. The radius of curvature of the prepared concave surface of the optical fiber is 800 μm, and the effective cavity mirror diameter is 45 μm. Both the plane mirror and the optical fiber concave mirror are coated with a distributed Bragg reflector type anti-reflection coating, and the reflectivity at 606 nm is 99%, while the reflectivity at 580 nm is different. Among them, the reflectivity of the plane mirror at 580 nm is 96.5%, and the reflectivity of the optical fiber concave mirror at 580 nm is 99.9%. The finesse of the optical fiber microcavity is 180.

[0044] According to embodiments of the present invention, the fiber microcavity has a cavity length on the order of hundreds of micrometers or less, for example, ranging from 0.1 micrometers to 900 micrometers. This allows for a larger cavity resonance linewidth, thereby increasing the storage bandwidth of solid-state quantum memory devices based on the fiber microcavity and enabling temporal multimode multiplexing. Due to the large cavity resonance linewidth, time-division multiplexing technology can be used to support temporal multimode storage. The volume of the fiber microcavity is one ten-thousandth of a cubic millimeter or less, enabling integrated applications. The fiber concave mirror of the fiber microcavity utilizes fiber array technology to divide a rare-earth ion-doped crystal film into multiple small storage units based on the fiber array, enabling integrated quantum memory. The thickness of the rare-earth ion-doped crystal film is on the order of hundreds of micrometers or less, for example, ranging from 0.1 micrometers to 900 micrometers. This ensures uniform stress and broadband modulation of the light absorption frequency of the rare-earth ion-doped crystal film under the action of a thin-film stress modulation device. High pressure is generated under low stress, and the light absorption frequency can be widely controlled by the thin-film stress modulation device. Under the action of the film stress regulating device, the frequency regulating range of the rare earth ion doped crystal film exceeds the non-uniform broadening of the rare earth ion doped crystal itself.

[0045] For example, the fiber microcavity has a length of 300 μm and a resonance linewidth of 3 GHz. Time division multiplexing technology is used to achieve time multi-mode storage. The volume of the fiber microcavity is 4×10 -5 mm 3 .

[0046] According to an embodiment of the present invention, a cavity length locking system includes a cavity length adjustment device, a photodetector, a servo feedback device and a broadband amplifier; the photodetector is used to detect the reflected light signal of the reference light coupled into the optical fiber microcavity, and input the reflected light signal as an error signal into the servo feedback device; the servo feedback device is used to output an adjustment signal according to the error signal, and send the adjustment signal to the broadband amplifier; the broadband amplifier is used to amplify the adjustment signal, and send the amplified adjustment signal to the cavity length adjustment device; the cavity length adjustment device is fixedly connected to the pigtail at the end face of the optical fiber; the cavity length adjustment device is used to adjust the distance between the end face of the optical fiber and the plane mirror according to the amplified adjustment signal.

[0047] According to an embodiment of the present invention, a cavity length locking system uses a specified active feedback technique based on a reference light source to adjust and lock the cavity length of a fiber microcavity. To resonate the signal light within the fiber microcavity, the cavity length must be adjusted. Therefore, a reference light source is first injected into the cavity, and the cavity length is adjusted to cause the signal light to resonate within the cavity, locking the cavity length at that point. Furthermore, when the frequency of the signal light changes, the reference light frequency is varied to adaptively adjust the cavity length of the fiber microcavity, thereby enabling resonance of signal light of different frequencies within the cavity. Furthermore, this enables high-efficiency quantum storage of signal light of varying frequencies. A rare earth ion-doped crystal film uses a film stress adjustment device to alter its absorption frequency for signal light, while the cavity length locking system alters its resonant frequency for signal light, jointly enabling high-efficiency quantum storage of signal light of varying frequencies. The specified active feedback technique is preferably Pound-Drever-Hall locking, although side-of-fringe locking may also be used.

[0048] According to an embodiment of the present invention, the cavity length adjustment device is preferably a stacked shear piezoelectric ceramic, and the tail portion of the fiber concave mirror in the fiber microcavity is fixed to the cavity length adjustment device using glue. In the side-of-fringe locking technique, the reference light detected by the photodetector is coupled into the reflected light signal of the fiber microcavity, which is input as an error signal to the servo feedback device. The output signal processed by the servo feedback device is amplified by a broadband amplifier and output to the cavity length adjustment device.

[0049] According to an embodiment of the present invention, the thin film stress adjustment device is preferably a shear piezoelectric ceramic with a central hole. The surface of the rare earth ion-doped crystal film coated with the anti-reflection film is glued to the thin film stress adjustment device. The thin film stress adjustment device can adjust the shear stress applied to the rare earth ion-doped crystal film by applying different voltages. Based on the principle of piezoelectric spectroscopy, a stress of 10N can produce a 5GHz optical absorption frequency shift in this rare earth ion-doped crystal film. After the thin film stress adjustment device is applied, the optical absorption center of the rare earth ion-doped crystal film at 3.5K corresponds to the frequency of the signal light.

[0050] According to an embodiment of the present invention, the optical fiber microcavity adopts a plano-concave cavity structure, which can achieve high-efficiency mode matching of the optical fiber microcavity to the signal light, facilitating the absorption of the signal light by the microcavity storage unit. The optical fiber microcavity combined with the rare-earth-doped crystal thin film can achieve high-efficiency impedance matching of the optical fiber microcavity to the signal light based on the specific absorption band prepared by the pump light. Combined with high-efficiency mode matching, it is conducive to achieving complete absorption of the signal light by the microcavity storage unit. The rare-earth ion-doped crystal thin film is obtained from a large piece of rare-earth ion-doped crystal using a physical polishing and thinning method, which can retain the excellent optical coherence properties of the large piece of rare-earth ion-doped crystal at low temperatures.

[0051] According to an embodiment of the present invention, the rare earth ion doped crystal film can be a europium doped yttrium silicate film, which is purified with an isotope concentration of 0.07%. 151 Eu 3+ The absorption coefficient of the europium-doped yttrium silicate crystal is 4.6 per centimeter. This europium-doped yttrium silicate crystal can be thinned and polished by physical means, preferably with a lapping machine. The size of the prepared rare earth doped crystal film is 4×5×0.2 mm 3 The surface roughness is 0.2 nm. The microcavity storage unit can be placed in a cryogenic cavity refrigerated without a liquid helium compressor, keeping the rare earth-doped crystal film at a low temperature of around 3.5 K, ensuring its long optical coherence lifetime and spin energy level lifetime.

[0052] According to an embodiment of the present invention, the fiber microcavity-based solid-state quantum storage device further includes a detection unit; the detection unit is configured to receive stored signal light output from the microcavity storage unit, count the cumulative amount of stored signal light over a period of time, and extract quantum bit information from the stored signal light.

[0053] According to an embodiment of the present invention, the light generating unit includes a first laser, a second laser, an acousto-optic modulator, a signal light source, and a feedback optimization system; the first laser is used to generate reference light; the second laser is used to generate initial laser light; the signal light source is used to generate signal light; the acousto-optic modulator is used to modulate the initial laser light to obtain pump light; the feedback optimization system is used to adjust the parameters of the pump light based on the principle of atomic frequency comb dephasing according to the cumulative amount of stored signal light determined by the detection unit over a period of time, thereby further improving the quantum storage efficiency of the signal light by reducing the atomic frequency dephasing.

[0054] According to an embodiment of the present invention, a solid-state quantum storage device based on a fiber microcavity includes a debugging phase and a storage phase. During the debugging phase, the solid-state quantum storage device based on a fiber microcavity also includes a signal light acousto-optic modulator (AOM). The AOM is used to modulate the initial laser to obtain signal light. A first laser generates a reference light with a linewidth within a specified range and a tunable frequency, and outputs the reference light to a microcavity storage unit for adjusting and locking the fiber microcavity length. A second laser generates a laser with a linewidth within a specified range and a frequency within a specified range. The AOM modulator modulates the laser light generated by the second laser to generate the pump light required for the microcavity storage unit, and outputs the pump light to the microcavity storage unit. The signal light AOM modulates the laser light generated by the second laser to generate the signal light carrying the quantum bits to be stored, and outputs the signal light to the microcavity storage unit. Using signal light generated by a signal light acousto-optic modulator, parameters of a fiber-microcavity-based solid-state quantum storage device under different signal light conditions are obtained, such as parameters of the reference light, parameters of the pump light, the cavity length of the fiber-microcavity, and the voltage of the thin-film stress adjustment device. The parameters of the fiber-microcavity-based solid-state quantum storage device under different signal light conditions obtained during the debugging phase are stored. Thus, during the storage phase, the parameters of the fiber-microcavity-based solid-state quantum storage device can be adjusted according to the signal light generated by the signal light source, thereby achieving storage of the signal light during the storage phase. Furthermore, corresponding parameter values of the fiber-microcavity-based solid-state quantum storage device, such as parameters of the reference light, parameters of the pump light, the cavity length of the fiber-microcavity, and the voltage of the thin-film stress adjustment device, are achieved for different signal light conditions.

[0055] According to an embodiment of the present invention, the feedback optimization system can select a simulated annealing algorithm controlled by a computer program. The feedback optimization system can be connected to the single photon counting and time correlation device under the control detection unit and the arbitrary waveform generator under the acousto-optic modulator.

[0056] According to an embodiment of the present invention, the wavelength difference between the lasers generated by the first laser and the second laser is greater than 5 nanometers, that is, the wavelength difference between the reference light and the initial laser is greater than 5 nanometers. This setting is to enable them to be effectively separated from each other by an optical filter device.

[0057] In the present invention, the linewidth within a specified range can be below 10kHz. The frequency of the second laser is within a specified range, related to the optical transition frequency of the selected rare earth ion-doped crystal film. The first laser can be a frequency-doubled semiconductor laser, which outputs a 606nm stabilized laser with a power of 900mW and a linewidth of the order of 1kHz. The laser is locked to a temperature-controlled optical reference cavity using Pound-Drever-Hall frequency locking technology, overcoming long-term drift caused by temperature changes and enhancing the stability of the system's continuous operation.

[0058] The second laser can be a frequency-doubled semiconductor laser, which outputs a stable 580nm laser with a power of 900mW and a linewidth of 1kHz. This laser frequency resonates with the optical absorption band of europium-doped yttrium silicate crystals. The laser is locked to a temperature-controlled optical reference cavity using Pound-Drever-Hall frequency locking technology, overcoming long-term drift caused by temperature changes and enhancing the stability of the system during continuous operation.

[0059] Both the AOM and the signal light AOM include an arbitrary waveform generator, an RF amplifier, and an AOM optical path. The AOM can be configured with a 200 MHz center frequency, while the signal light AOM can be configured with a 200 MHz center frequency. The signal light AOM modulates and generates signal light carrying time-bin quantum bits, with a light field frequency of 200 MHz.

[0060] According to an embodiment of the present invention, the detection unit includes a chopping device, a filtering device, a projection-based measurement device, and a single-photon counting and time correlation device; the chopping device is used to remove the pump light in the optical signal output from the microcavity storage unit to obtain a detection light signal; the filtering device is used to filter out the reference light in the detection light signal to obtain the stored signal light; the projection-based measurement device is used to extract the quantum bit information from the stored signal light; the single-photon counting and time correlation device is used to perform single-photon detection on the signal light after the quantum bit information is extracted, and to count the cumulative number of signal lights after the quantum bit information is extracted within a period of time.

[0061] According to an embodiment of the present invention, the chopping device can be a mechanical optical shutter switch; the filtering device can be a 580nm bandpass narrowband filter; and the single-photon counting and time correlation device can be an avalanche silicon-based detector and a time-correlated single-photon counter. A projection-based measurement device can be used before the single-photon counting and time correlation device, and then the single-photon counting and time correlation device can be used to detect the bit information of the signal light to be stored and read out.

[0062] According to an embodiment of the present invention, the ratio of the sum of the single-photon counts and the time-correlated photon histogram of the signal light detected by the time correlation device when the fiber microcavity is detuned, and the sum of the single-photon counts and the time-correlated photon histogram of the stored signal light detected by the time correlation device when the fiber microcavity is resonant (not detuned), is the signal light access efficiency. This value is output to the feedback optimization system in the combing parameter optimization mode, and the feedback optimization system adjusts the pump light pulse parameters based on this ratio.

[0063] In the case of detuning of the optical fiber microcavity, the number of prepared signal lights can be used as the statistical value of a time-correlated photon statistical histogram of the signal light detected by the detection unit. When the optical fiber microcavity achieves resonance (no detuning), the statistical value of the number of signal lights detected by the detection unit is used to obtain the ratio of the sum of the two counts. When the access efficiency of the signal light is low, that is, when the ratio of the number of stored signal lights to the number of prepared signal lights is less than a preset value, it is considered that the pulse parameters of the pump light need to be adjusted to improve the access efficiency.

[0064] Since the number of prepared signal lights can be used as the statistical value of the time-correlated photon statistical histogram of the signal light detected by the detection unit, it can be considered that the number of prepared signal lights is known. Instead of detection, the statistical value of the number of stored signal lights detected by the detection unit can be directly obtained, and the pulse parameters of the pump light can be adjusted based on the statistical value.

[0065] Figure 2 A structural block diagram of a solid-state quantum storage device based on an optical fiber microcavity according to another embodiment of the present invention is shown.

[0066] like Figure 2 As shown in the figure, a fiber-based solid-state quantum storage device in the debugging stage is used as an example to describe the fiber-based solid-state quantum storage device. The fiber-based solid-state quantum storage device includes: a light generating unit 11, a microcavity storage unit 12, and a detection unit 13. The light generating unit 11 is used to generate the pump light and reference light required by the microcavity storage unit 12, prepare the signal light carrying the quantum bits to be stored, and output the pump light, reference light, and signal light to the microcavity storage unit 12.

[0067] The optical generation unit 11 includes a first laser 111, a second laser 112, an acousto-optic modulator (AOM) 113, a signal light AOM 114, and a feedback optimization system 115. The first laser 111 is used to generate reference light with a linewidth within a specified range and a tunable frequency to lock the cavity length of the optical fiber microcavity, and output the reference light to the microcavity storage unit 12. The second laser 112 is used to generate laser light with a linewidth within a specified range and a frequency within a specified range. The AOM 113 is used to modulate the pump light required by the microcavity storage unit 12 based on the laser light generated by the second laser 112, and output the pump light to the microcavity storage unit 12. The signal light AOM 114 is used to modulate the signal light carrying the quantum bits to be stored based on the laser light generated by the second laser 112, and output the signal light to the microcavity storage unit 12. The feedback optimization system 115 is used to feedback optimize the pump light generated by the AOM 113 based on the readout efficiency of the signal light detected by the detection unit 13 after storage.

[0068] The microcavity storage unit 12 comprises a fiber microcavity 121, a rare-earth ion-doped crystal film 122, a spring damping platform 1231, a cavity length locking system 1232, and a film stress adjustment device 1233. The fiber microcavity 121 is an open Fabry-Perot cavity composed of a microscopic fiber concave mirror and a macroscopic plane mirror. It is used to enhance the interaction between signal light and the rare-earth ion-doped crystal film 122. The rare-earth-doped crystal film 122 absorbs signal light based on a specific absorption band created by pump light and releases it after a specified time. The spring damping platform 1231 isolates the effects of vibration on the cavity length of the fiber microcavity 121. The cavity length locking system 1232 adjusts and locks the cavity length of the fiber microcavity 121 using a specified feedback technique based on reference light. The film stress adjustment device 1233 is used to change the absorption frequency of the rare-earth ion-doped crystal film for signal light by adjusting the stress applied to the rare-earth ion-doped crystal film based on the piezoelectric spectroscopy effect.

[0069] The detection unit 13 includes a chopping device 131, a filtering device 132 and a single-photon counting and time correlation device 133; the chopping device 131 is used to separate the pump light in the time domain; the filtering device 132 is used to separate the reference light in the frequency domain; the single-photon counting and time correlation device 133 is used to perform single-photon detection on the signal light read out after storage and complete time-correlated photon counting statistical analysis.

[0070] When the fiber microcavity-based solid-state quantum storage device is in the storage stage, the difference from the fiber microcavity-based solid-state quantum storage device in the debugging stage is mainly reflected in that the signal light is output by the signal light light source instead of being implemented by the signal light acousto-optic modulator 114, which will not be further described here.

[0071] exist Figure 2In the figure, the dotted arrows indicate the objects of action, namely, the cavity length locking system 1232 regulating the fiber microcavity 121, the film stress adjustment device 1233 regulating the rare earth ion-doped crystal film 122, the spring damping platform 1231 regulating the fiber microcavity 121, the single photon counting and time correlation device 133 regulating the feedback optimization system 115, and the feedback optimization system 115 regulating the acousto-optic modulator 113. Specifically, the dotted arrow between the film stress adjustment device 1233 and the rare earth ion-doped crystal film 122 indicates that the film stress adjustment device 1233 applies stress to the rare earth ion-doped crystal film 122, the dotted arrow between the cavity length locking system 1232 and the fiber microcavity 121 indicates that the cavity length locking system 1232 adjusts the cavity length of the fiber microcavity 121, and the dotted arrow between the spring damping platform 1231 and the fiber microcavity 121 indicates that the spring damping platform 1231 isolates the influence of vibration on the cavity length of the fiber microcavity 121. The single-photon counting and time correlation device 133 transmits the result of single-photon detection to the feedback optimization system 115. The feedback optimization system 115 determines the parameters of the pump light according to the result of single-photon detection, and the acousto-optic modulator 113 generates corresponding pump light according to the parameters of the pump light.

[0072] Figure 3 FIG2 shows a schematic diagram of component connections of a solid-state quantum storage device based on an optical fiber microcavity according to another embodiment of the present invention.

[0073] like Figure 3As shown, a fiber-based solid-state quantum storage device during the debugging phase is used as an example to describe the device. Light emitted by a second laser 112 is modulated by an acousto-optic modulator 113 and a signal-light acousto-optic modulator 114 to generate pump light and signal light. The signal light at this point is the signal light to be stored. The pump light and the signal light to be stored are first combined by a first optical beam splitter 116. After passing through a single-mode fiber, they are combined with the reference light generated by the first laser 111 and then by a 580 nm filter 14, which serves as a signal light wavelength filter. The single-mode fiber has a collimating fiber emitter. The reference light generated by the first laser 111 passes through the collimating fiber emitter and is reflected by a reflector 15 before being combined with the pump light and the signal light to be stored. Since the pump light and the signal light to be stored originate from the same single-mode emitter, they have the same spatial mode. The pump light, the signal light to be stored, and the reference light are then coupled into the fiber-based microcavity 121 through a lens assembly 16. The lens group 16 can be a lens group with a spherical aberration, and the mode matching efficiency can reach 99.9%. The film stress adjustment device 1233 in the microcavity storage unit 12 applies stress to the rare earth ion doped crystal film 122. Based on the piezoelectric spectroscopy effect, the light absorption frequency of the rare earth ion doped crystal film 122 is changed, and the center frequency of the light absorption frequency is made consistent with the frequency of the signal light to be stored. The signal light to be stored will be fully absorbed by the rare earth ion doped crystal film 122, and after a period of time, the stored signal light is released in a manner that propagates in the opposite direction to the signal light to be stored. The stored signal light can be extracted by the second optical beam splitter 117, and after passing through the chopping device 131 and the filtering device 132, it is detected by the single photon counting and time correlation device 133. In order to extract the stored signal light without loss, the second optical beam splitter 117 can be replaced with a Faraday rotator and an optical polarization beam splitter, and the stored signal light is extracted using the polarization dimension of the light.

[0074] The fiber-microcavity-based solid-state quantum storage device also includes a pump light chopper 118. Pump light chopper 118 is turned on when pump light is emitted, while chopper 131 is turned off, to achieve pump light absorption band preparation and protect the detection unit. When signal light is emitted, pump light chopper 118 is turned off, while chopper 131 is turned on. Because the pump light is relatively strong, the shutoff function of the acousto-optic modulator 113 is insufficient, and some pump photons may leak into the microcavity storage unit and the detection unit. Although the leaked light is extremely weak and invisible to the naked eye, it is still fatal to the detection unit, which detects single-photon signal light. A second optical beam splitter 117 is used to separate the stored optical signal output from the microcavity storage unit from the signal photon to be stored. The stored signal light and the signal light to be stored are collinear in the optical path, but in opposite directions. The signal light to be stored is destined for the storage unit, while the stored signal light is returned from the microcavity storage unit. Complete separation can be achieved through polarization.

[0075] Figure 4 A timing diagram of the storage process of a solid-state quantum storage device based on an optical fiber microcavity according to another embodiment of the present invention is shown.

[0076] like Figure 4 As shown, before the storage process, the cavity length locking system locks the cavity length, causing the reference light to resonate with the fiber microcavity. Adjusting the frequency of the reference light generated by the first laser synchronously changes the cavity length of the fiber microcavity, finding a specific frequency value for the reference light and causing the signal light to resonate with the fiber microcavity. Adjusting the voltage of the thin film stress adjustment device synchronously changes the optical absorption frequency of the rare earth ion-doped crystal thin film, finding a specific voltage value for the film stress adjustment device so that the center frequency of the optical absorption frequency of the rare earth ion-doped crystal thin film coincides with the frequency of the signal light. During the storage process, the pump light modulated by the acousto-optic modulator (AOM) is repeatedly used with different swept pulses to initialize the energy level population and prepare the atomic frequency comb. The atomic frequency comb preparation pulses are preferably parallel complex hyperbolic secant swept pulses. The signal light AOM modulates the signal light to a specific time pattern and outputs it to the microcavity storage unit. After a specific time, the microcavity storage unit releases the stored signal light. This specific time is related to the atomic frequency comb preparation parameters. In the combing parameter optimization mode, the feedback optimization system can feedback optimize the pulse parameters of the atomic frequency comb pulses prepared by the pump light modulated by the acousto-optic modulator based on the cumulative count of the stored signal light detected by the detection unit during the storage process over a period of time.

[0077] The storage efficiency η of the cavity-enhanced atomic frequency depletion scheme can be simplified as:

[0078] .

[0079] Among them, η Mis the mode matching efficiency of the signal light coupled into the fiber microcavity, η deph represents the efficiency loss caused by the phase loss of the atomic frequency scheme, ε and represent the additional loss of the light field traveling back and forth within the cavity and the effective absorption depth of the rare earth ion-doped crystal film, respectively.

[0080] When the ratio of the film absorption to the additional loss of the cavity If the comb tooth fineness, one of the preparation parameters of the atomic frequency comb, is higher than 10 and higher than 5, the expected theoretical storage efficiency is over 75%.

[0081] The above describes embodiments of the present invention. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A solid-state quantum storage device based on an optical fiber microcavity, characterized in that: The fiber microcavity-based solid-state quantum storage device includes: a light generating unit and a microcavity storage unit; The light generating unit is used to generate pump light, reference light and signal light, and transmit the pump light, the reference light and the signal light to the microcavity storage unit; wherein the signal light carries the quantum bit information to be stored; The microcavity storage unit is used to realize quantum storage of signal light of different frequencies; The microcavity storage unit includes an optical fiber microcavity, a rare earth ion doped crystal film and an adjustment system; The rare earth ion doped crystal film is arranged inside the optical fiber microcavity; the rare earth ion doped crystal film is used to store the signal light; The pump light generates a specific absorption band corresponding to the parameters of the pump light on the rare earth ion-doped crystal film according to an atomic frequency comb scheme, so as to adjust the storage time of the signal light; The adjustment system is used to apply stress to the rare earth ion-doped crystal film, and based on the piezoelectric spectroscopy effect, change the light absorption frequency of the rare earth ion-doped crystal film, so that the center frequency of the light absorption frequency is consistent with the frequency of the signal light. It is also used to adjust the cavity length of the optical fiber microcavity to a cavity length corresponding to the frequency of the reference light according to the frequency of the reference light, so as to lock the cavity length of the optical fiber microcavity, thereby achieving resonance of the signal light in the optical fiber microcavity and isolating the influence of vibration on the cavity length of the optical fiber microcavity.

2. The solid-state quantum storage device based on optical fiber microcavity according to claim 1, characterized in that: The optical fiber microcavity comprises an optical fiber concave mirror and a plane mirror; the optical fiber concave mirror and the plane mirror form an open Fabry-Perot cavity.

3. The solid-state quantum storage device based on optical fiber microcavity according to claim 2, characterized in that: The rare earth ion doped crystal film includes an inner surface and an outer surface; the inner surface is the surface facing the optical fiber concave mirror; the outer surface is the surface opposite to the inner surface; The plane mirror is obtained by coating the outer surface of the rare earth ion doped crystal film with an optical reflection enhancement film.

4. The solid-state quantum storage device based on optical fiber microcavity according to claim 1, characterized in that: The adjustment system includes a cavity length locking system and a spring shock-absorbing platform; The cavity length locking system is used to adjust the cavity length of the fiber microcavity to a cavity length corresponding to the frequency of the reference light according to the frequency of the reference light, so as to lock the cavity length of the fiber microcavity, and to actively isolate the influence of vibration on the cavity length of the fiber microcavity and realize the resonance of the signal light in the fiber microcavity; The spring damping platform is used to isolate the influence of vibration on the cavity length of the optical fiber microcavity in a passive manner.

5. The solid-state quantum storage device based on optical fiber microcavity according to claim 4, characterized in that: The adjustment system also includes a film stress adjustment device; The film stress adjustment device is arranged on the outer surface or inner surface of the rare earth ion doped crystal film; The film stress adjustment device is used to apply stress to the rare earth ion doped crystal film, based on the piezoelectric spectroscopy effect, to change the light absorption frequency of the rare earth ion doped crystal film, and make the center frequency of the light absorption frequency consistent with the frequency of the signal light.

6. The fiber microcavity-based solid-state quantum storage device according to claim 1, characterized in that: The fiber microcavity-based solid-state quantum storage device further includes a detection unit; The detection unit is used to receive the stored signal light output from the microcavity storage unit, count the cumulative number of the stored signal light within a period of time, and extract quantum bit information from the stored signal light.

7. The fiber microcavity-based solid-state quantum storage device according to claim 6, characterized in that: The light generating unit includes a first laser, a second laser, an acousto-optic modulator, a signal light source and a feedback optimization system; The first laser is used to generate the reference light; The second laser is used to generate initial laser; The signal light source is used to generate signal light; The acousto-optic modulator is used to modulate the initial laser to obtain the pump light; The feedback optimization system is used to adjust the parameters of the pump light according to the cumulative amount of the stored signal light determined by the detection unit within the period of time and based on the atomic frequency comb dephasing principle.

8. The fiber microcavity-based solid-state quantum storage device according to claim 6, characterized in that: The detection unit includes a chopping device, a filtering device, a projection-based measurement device, and a single-photon counting and time correlation device; The chopping device is used to remove the pump light from the optical signal output from the microcavity storage unit to obtain a detection optical signal; The filtering device is used to filter out the reference light in the detection light signal to obtain the stored signal light; The projection-based measurement device is used to extract the quantum bit information in the stored signal light; The single-photon counting and time correlation device is used to perform single-photon detection on the signal light after the quantum bit information is extracted, and to count the cumulative number of the signal light after the quantum bit information is extracted within the period of time.

9. The fiber microcavity-based solid-state quantum storage device according to claim 1, characterized in that: The cavity length of the optical fiber microcavity is set to range from 0.1 microns to 900 microns to increase the cavity resonance linewidth; the increased cavity resonance linewidth improves the storage bandwidth of the solid-state quantum storage device based on the optical fiber microcavity, thereby realizing temporal multi-mode multiplexing.

10. The fiber microcavity-based solid-state quantum storage device according to claim 5, characterized in that: The thickness of the rare earth ion doped crystal film is set to range from 0.1 micrometers to 900 micrometers, so that the stress of the rare earth ion doped crystal film is evenly distributed under the action of the film stress regulating device.

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