Apparatus, method, and system for scalable optical cavity locking

Abstract

Apparatus, systems, and methods for stabilizing the lengths of a plurality of optical cavities are provided according to aspects of the present disclosure. The apparatus comprises an optical light source configured to output an incident light beam. The apparatus also includes a separation means configured to receive the incident light beam output from the optical source and to split the received incident light beam to output two or more light beams. The apparatus further comprises a plurality of optical cavities, each of the plurality of optical cavities configured to receive one of the light beams output from the separation means and to transmit or reflect a portion of the light indicating whether the optical cavity is in resonance with the light source. Each optical cavity is also configured to contain a matter qubit within the optical cavity. Each matter qubit is configured to capture a photon and disperse quantum entanglement, the rate of entanglement being increased by the Purcell effect. Each optical cavity is further configured to be connected to an actuator. The actuator is configured to adjust the length of the optical cavity based on a portion of the light transmitted through or reflected from the optical cavity so as to be in resonance with the optical source in order to lock the optical cavity to the optical source. The material qubit is the same for each optical cavity. For each optical cavity, the incident light beam is detuned from the transition wavelength of the material qubit by a ratio of two integers a and b, where a / b represents a fixed fraction, to ensure that there is at least one point within the actuator's range of motion where the double resonance condition is satisfied, such that the optical cavity resonates simultaneously with the material qubit and the incident light beam.

Description

[Technical Field]

[0001] This disclosure relates to an apparatus, system, and method for simultaneously locking or stabilizing the lengths of multiple optical cavities. This disclosure finds useful, for example, in various quantum networking and quantum computing schemes. [Background technology]

[0002] Optical cavities containing material qubits are considered crucial components in the development of quantum computing and quantum networking devices because they allow for control over the state of the qubits within the optical cavity. Material qubits trap photons and distribute quantum entanglement throughout the quantum system.

[0003] An optical cavity is a device that forms a resonator by restricting light along a closed path using reflective optical elements. It is a resonator that supports only light of a specific frequency / wavelength. The wavelength of light supported by an optical cavity depends on the length of the optical cavity. Specifically, light can enter the optical cavity only if the length of the optical cavity is an integer multiple of the wavelength of light. Light of a wavelength other than the correct one is reflected from the cavity. Therefore, for an optical cavity to be used in practical applications, its length must be reliably adjusted and locked.

[0004] Creating a functional quantum computing or networking system requires the use of multiple optical cavities, all of which must be locked. Currently, locking or stabilizing the length of optical cavities typically requires components that can be bulky and / or expensive. Locking multiple optical cavities necessitates duplicating these expensive and bulky components. The cost and space required for these components thus limit the practical applications currently possible using optical cavities.

[0005] This disclosure was conceived in the context described above. [Overview of the Initiative]

[0006] In one embodiment, a device is provided for stabilizing the lengths of multiple optical cavities. The device includes an optical light source configured to output an incident light beam. The device also includes a separation means configured to receive the incident light beam output from the optical source and to split the received incident light beam to output two or more light beams. The device further includes multiple optical cavities, each of which is configured to receive one of the light beams output from the separation means and to transmit or reflect a portion of the light indicating whether the optical cavity is in resonance with the optical light source. Each optical cavity is also configured to contain a matter qubit within the optical cavity. Each matter qubit is configured to capture a photon and disperse quantum entanglement, the rate of entanglement being increased by the Purcell effect. Each optical cavity is further configured to be connected to an actuator. The actuator is configured to adjust the length of the optical cavity based on a portion of the light transmitted through or reflected from the optical cavity so that it is in resonance with the optical source, in order to lock the optical cavity to the optical source. The matter qubit is the same for each optical cavity. For each optical cavity, the incident light beam is detuned from the transition wavelength of the material qubit by a ratio of two integers a and b, where a / b represents a fixed fraction, so that there is at least one point within the actuator's range of motion where the double resonance condition is satisfied, such that the optical cavity resonates simultaneously with the material qubit and the incident light beam.

[0007] Advantageously, by providing separation means between multiple optical cavities and optical light sources, the length of each optical cavity can be stabilized simultaneously. Even more advantageously, there is no need to provide a separate optical light source or other equipment for each optical cavity. This reduction in component duplication reduces both the cost of the equipment and the amount of space required to accommodate all of it.

[0008] Furthermore, detuning the incident light beam from the material qubit wavelength ensures that undesirable excitation of the material qubit is prevented and that the incident light beam can be filtered out of the path of entangled photons.

[0009] An optical cavity is said to be in a resonant state or resonating if its length is a half-integer multiple of its wavelength. To lock the cavity length using an incident light beam of one wavelength and enhance a matter qubit at a different wavelength, this condition must therefore be satisfied at both wavelengths, i.e., there is a double resonance condition. That is, the double resonance condition is satisfied when the optical cavity resonates with both the wavelength of the photons emitted from the matter qubit and the lock wavelength.

[0010] When any wavelength of incident light beam is used, it is impossible to guarantee that there is a single cavity length that satisfies the double resonance condition. By introducing a small degree of adjustability to the initial arbitrary wavelength, the system can be adjusted to ensure that there is a single point where the double resonance condition is satisfied. Furthermore, to stabilize the lengths of multiple optical cavities using a single optical light source that outputs an incident light beam at an initial arbitrary wavelength adjustable within up to one free spectral range, all optical cavities must initially have the same length, at least within the adjustment tolerance of the actuator. Engineering this using standard manufacturing processes is difficult.

[0011] However, this problem can be solved by restricting the selection of the incident light beam wavelength to a fixed ratio of the wavelength of the material qubit. Thus, not all optical cavities need to have the same length initially. For example, if the incident light beam is selected to have half the wavelength of the photons emitted from the material qubit, it can be ensured that all emitter resonances have corresponding lock resonances. The wavelength of the incident light beam is not limited to half the wavelength of the emitted photons, and any fixed fraction or multiple of the wavelength of the incident light beam that is guaranteed to repeat within the range of movement of the actuator can be used.

[0012] Advantageously, this configuration provides a cost-effective and compact way to stabilize multiple optical cavities, particularly for applications requiring a very large number of stable optical cavities (such as data centers). This is especially useful when the required wavelength of light is far from a conveniently stable reference wavelength, such as the wavelength obtained from transitions of neutral atoms, because stable optical light sources can be very expensive. Therefore, providing a separate, sufficiently stable optical light source for each and every optical cavity may not be economically feasible. In addition, each optical light source requires an offset lock, which typically requires high-frequency electronics that are expensive and difficult to engineer. Increasing the number of optical cavities that can be locked using a single optical light source results in a chain reaction of cost and space savings.

[0013] Optionally, the apparatus may further include a first modulator positioned between the separation means and the optical cavity for each of the multiple optical cavities.

[0014] Advantageously, providing a modulator between the separation means and the optical cavity allows the wavelength of the lock light emitted by the optical light source to be individually fine-tuned for each cavity. Manufacturing tolerances mean that each optical cavity is likely to be slightly different. In addition, the material qubit wavelength and the incident light beam wavelength may interact with the mirrors of the optical cavity in slightly different ways. These differences may affect the cavity length experienced by each of the material qubit wavelength and the incident light beam wavelength.

[0015] The modulator applies a phase shift to the frequency of the incident light beam to account for optical effects and manufacturing tolerances. Each optical cavity has a corresponding modulator. This ensures that each optical cavity continues to resonate simultaneously with both the material qubit and the incident light beam. Thus, multiple optical cavities can still be locked simultaneously, even though the optical cavities are not identical.

[0016] The first modulator may include an acousto-optic modulator (AOM) or an electro-optic modulator (EOM).

[0017] The apparatus may also include a second modulator positioned between the optical light source and the separation means to apply a phase shift to the incident light beam. The second modulator is an EOM (Energy-Oriented Modulator).

[0018] The apparatus may also include a second separation means positioned between the optical light source and the second modulator to split the incident light beam into multiple light beams.

[0019] Advantageously, this makes it possible to adjust or stabilize a larger number of optical cavities simultaneously. The number of optical cavities that can be locked is limited by the amount of light that can be output by a single EOM and the minimum amount of light required by each optical cavity. As the amount of light received by the optical cavities decreases, the noise experienced by the connected electronics forms a larger proportion of any detected signal. Too little light reduces the signal-to-noise ratio of the locked signal. This degradation leads to a decrease in the robustness of the cavity lock. When the maximum transmission power of light through the EOM is reached, more EOMs are required. Splitting the incident light beam using a second separation means between the optical light source and the EOM allows light from the optical light source to be sent to multiple EOMs, which can then be used to stabilize the lengths of multiple optical cavities. Thus, the use of a second separation means advantageously makes it possible to reliably stabilize and lock the lengths of many optical cavities using a single stable optical light source. This minimizes the cost and space requirements of the equipment needed to lock a larger number of optical cavities.

[0020] The apparatus may also include measuring means for measuring the proportion of light that has passed through or been reflected from each optical cavity.

[0021] The apparatus may also include means for scanning each actuator.

[0022] The wavelength of the incident light beam is λ l = λ q *a / b, where a < N, and λ q is the transition wavelength of the material qubit and is fixed, and λ l is the wavelength of the incident light beam, N = z / λ q where N is a number greater than 1 and not necessarily an integer, z is the movement range of the actuator, and a and b are the integers according to claim 1, and a / b is a simplified fraction.

[0023] The ratio at which the incident light beam is detuned from the wavelength of the material qubit can include two integers less than 10. The ratio can include two integers less than 5. The ratio of the wavelength of the incident light beam to the wavelength of the material qubit can be 1:2, 2:3, 3:4, 4:5, 2:1, 3:2, 4:3, or 5:4. Advantageously, these ratios make it possible to keep the wavelength of the incident light beam within the most easily handled range in the actual situation. Further, typically, it is easy to procure a part that handles or emits light within this wavelength range.

[0024] The wavelength of the incident light beam can be within the range of 600 to 1600 nm. Advantageously, this wavelength range is the easiest to use in the actual situation as described above.

[0025] The separation means can be an optical splitter, the material qubit can include neutral atoms or trapped ions, the actuator can be a piezo actuator, and the optical light source can be a laser. Advantageously, since all of these are standard components on site, there is no need to procure or use special dedicated or rare equipment. This minimizes cost and usage complexity.

[0026] Each of the optical cavities can include a double band coating. Advantageously, this enables each optical cavity to reflect at both the lock (incident light beam) wavelength and the material qubit transition wavelength.

[0027] The apparatus may also include, for each optical cavity, a locking mechanism for maintaining the length of the optical cavity. Advantageously, this ensures that the length of the optical cavity remains stable and compensates for any thermal or vibrational shifts.

[0028] The actuator may be configured to lock each optical cavity into a resonant state with the optical light source using pound-drever-hall technology, side-of-peak technology, or dither locking technology.

[0029] The apparatus may be intended for use in quantum computing and / or quantum networking applications. Stabilizing the lengths of multiple optical cavities is a requirement for various quantum computing and networking schemes. Therefore, providing an apparatus that performs this function for use in this field would favorably facilitate research and practical applications in these fields.

[0030] The apparatus may also include stabilization means for stabilizing the optical light source. The stabilization means may generate fixed-fraction locked light at a fixed fractional wavelength using a reference that is stable at the qubit transition wavelength.

[0031] Advantageously, the stabilization means ensure that the wavelength of light emitted from the optical light source remains stable. By ensuring that the optical light source is stable, the length of the optical cavity can be more reliably stabilized.

[0032] The stabilization means may include a second harmonic generator or optical transmission cavity for generating fixed fractional locked light.

[0033] Advantageously, a second harmonic generator or optical transmission cavity can be used to directly generate fixed fractional-locked light without requiring any form of optical light source offset locking. For example, if the material qubit in the optical cavity contains an alkali element, an atomic vapor cell can provide the exact qubit transition wavelength as a reference. This wavelength can then be halved to provide the wavelength of fixed fractional-locked light, and the second harmonic generator or optical transmission cavity can generate fixed fractional-locked light at this halved wavelength.

[0034] The optical light source can be stabilized by referencing an atomic vapor cell, a stabilized HeNe laser, or an optical frequency comb. The atomic vapor cell may include an Rb cell.

[0035] In another aspect of the present invention, a system for stabilizing the lengths of multiple optical cavities is provided. The system comprises at least two devices as described in any one of claims 1 to 14 and a reference optical source configured to output a reference incident light beam. The system further includes a reference separation means configured to receive the reference incident light beam output from the reference optical source and to split the received reference incident light beam to output two or more reference light beams, so that each optical light source of the at least two devices is stabilized with reference to one of the output reference light beams.

[0036] Advantageously, this increases the number of optical cavities that can be locked simultaneously. Once the maximum power of a single optical light source is reached, multiple optical light sources can be offset-locked relative to a stable single reference optical source.

[0037] In yet another aspect of the present invention, a method is provided for stabilizing the lengths of a plurality of optical cavities. The method comprises outputting an incident light beam by an optical light source. The method also comprises receiving the incident light beam output from the optical source in a separation means. The method also comprises splitting the received incident light beam by the separation means to output two or more light beams. The method also comprises, for each of the plurality of optical cavities, receiving one of the light beams output from the separation means, transmitting or reflecting a portion of the light indicating whether the optical cavity is in resonance with the optical light source, capturing photons with a material qubit located in the optical cavity to disperse quantum entanglement, the rate of entanglement being increased by the Purcell effect, and adjusting the length of the optical cavity by an actuator connected to the optical cavity based on a portion of the light transmitted through or reflected from the optical cavity so as to be in resonance with the optical source, in order to lock the optical cavity to the optical source. The material qubit is the same for each optical cavity, and for each optical cavity, the incident light beam is detuned from the transition wavelength of the material qubit by a ratio of two integers a and b, where a / b represents a fixed fraction, to ensure that there is at least one point within the range of movement of the actuator where the double resonance condition is satisfied, such that the optical cavity resonates simultaneously with the material qubit and the incident light beam.

[0038] The method may also include measuring a portion of the light using measuring means to determine the proportion of light that has passed through or been reflected from an optical cavity.

[0039] The method may also include locking the length of an optical cavity by a locking means when a determined percentage of transmitted or reflected light is within a predetermined range. Advantageously, this holds the length of the optical cavity. The length of the optical cavity may be locked by measuring when the determined percentage of transmitted light is maximum or when the determined percentage of reflected light is minimum. The optical cavity may be locked using pound-hold lever technology, side-of-peak lock technology, or dither-lock technology.

[0040] Those skilled in the art will likely come up with many modifications and other embodiments of the inventions described herein in light of the teachings presented herein. Therefore, it will be understood that the disclosure herein should not be limited to the specific embodiments disclosed herein. Furthermore, while the descriptions provided herein provide exemplary embodiments in the context of specific combinations of elements, steps and / or functions may be provided by alternative embodiments without departing from the scope of the invention. [Brief explanation of the drawing]

[0041] Herein, embodiments of the present invention are described only by reference to the accompanying drawings, in which similar reference numerals are used to depict similar parts. In the drawings,

[0042] [Figure 1] An embodiment of a device for locking multiple optical cavities according to an aspect of this disclosure is shown. [Figure 2] Another embodiment of a device for locking multiple optical cavities according to aspects of this disclosure is shown. [Figure 3] A graph showing the transmission of light through an optical cavity in one embodiment of the present invention is shown. [Figure 4] A method for stabilizing the lengths of multiple optical cavities according to an aspect of this disclosure is shown. [Figure 5] An embodiment of a system for locking multiple optical cavities according to aspects of this disclosure is shown. [Figure 6] Another embodiment of a device for locking multiple optical cavities according to aspects of this disclosure is shown. [Figure 7] Further embodiments of a device for locking multiple optical cavities according to aspects of this disclosure are shown. [Modes for carrying out the invention]

[0043] Embodiments of this disclosure are described below with reference to the accompanying drawings. However, it should be understood that this disclosure is not limited to embodiments, and all modifications and / or equivalents or substitutions thereof also fall within the scope of this disclosure. The same or similar reference numerals may be used to refer to the same or similar elements throughout the specification and drawings.

[0044] As used herein, the terms “have,” “may have,” “include,” and “may include” indicate the presence of a feature (e.g., number, function, operation, or component such as parts) and do not exclude the presence of other features.

[0045] As used herein, the terms “A or B,” “A and / or B,” or “one or more A and / or B” may include all possible combinations of A and B. For example, “A or B,” “A and B,” or “A or B,” may mean all of the following: (1) including at least one A, (2) including at least one B, or (3) including at least one A and at least one B.

[0046] As used herein, the terms “first” and “second” may modify various components, regardless of their materiality, and do not limit the components. These terms are used solely to distinguish one component from another. For example, “first user device” and “second user device” may refer to different user devices, regardless of the order or importance of the devices. For example, a first component may be referred to as a second component, and vice versa, without departing from the scope of this disclosure.

[0047] When an element (e.g., a first element) is described as being "combined with" or "connected to" another element (e.g., a second element) (mechanically, operationally, or communicatively), it will be understood that it may be combined with or connected to other elements directly or via a third element. In contrast, when an element (e.g., a first element) is described as being "directly combined with" or "directly connected to" another element (e.g., a second element), it will be understood that no other element (e.g., a third element) intervenes between the element and the other elements.

[0048] As used herein, the term “configured (or set up) to do something” may be used interchangeably with the terms “suitable to do something,” “capable to do something,” “designed to do something,” “adapted to do something,” “made to do something,” or “capable to do something,” depending on the context.

[0049] The singular forms "a," "an," and "the" should be understood to include plural references unless the context explicitly indicates otherwise.

[0050] Terms used herein are provided solely to describe some embodiments but do not limit the scope of other embodiments of the Disclosure. All terms used herein, including technical and scientific terms, have the same meaning as commonly understood by those skilled in the art to the extent of the embodiments of the Disclosure. Terms such as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0051] Referring here to the figures, Figure 1 shows a schematic diagram of a device 100 for locking a plurality of optical cavities according to an aspect of the present disclosure. The device 100 comprises an optical light source 102, a separation means 104, a plurality of optical cavities 106, each containing a material qubit 108, and a plurality of actuators 110.

[0052] An optical light source 102, which may be a laser, is configured to generate and output an incident light beam 112. The incident light beam 112 is received by a separation means 104, such as an optical splitter, which divides or splits the incident light beam 112 into a plurality of light beams 114. In this embodiment, the incident light beam 112 is split into four light beams 114, but this is illustrative, and the separation means 104 may divide or split the incident light beam 112 into any number of light beams 114. The light beams 114 have the same wavelength as the incident light beam 112. The light beams 114 may differ from the incident light beam 112 only in terms of their intensity, such that the intensity of the light beams 114 may be less than the intensity of the incident light beam 112 due to the incident light beam 112 being split into a plurality of light beams 114. Each light beam 114 may be transmitted into an optical cavity 106 to allow cavity stabilization.

[0053] An optical cavity 106 (also called an interface cavity or science cavity) is formed between a first reflective surface and a second reflective surface. The first and second reflective surfaces may be formed from the same or different substrates. Each substrate may be provided with a coating to improve the reflectivity of the surface. The coating may be a biband coating that allows the optical cavity 106 to reflect both the incident light beam wavelength 112 and the material qubit transition wavelength. Each optical cavity 106 may be arranged as a Fabry-Perot type cavity having a ripple structure, and at least one reflective surface is formed to have a concave mirror surface with a very high reflectivity at the wavelength of interest in a 99.9% region.

[0054] Providing an uneven cavity allows the trapped ion or neutral atom providing the material qubit 108 to be located in the center of the optical cavity 106 at the cavity waist, where the parcel enhancement effect is maximized. In this respect, the optical cavity 106 interacts with the material qubit 108 and provides an optical-matter interface for enhancing the transmission or absorption of a single photon by the material qubit 108. This facilitates photon manipulation and control of the material qubit 108, for example, to support the performance of qubit gate operations in a quantum computer.

[0055] A material qubit 108 is provided within an optical cavity 106. Each optical cavity 106 contains a material qubit 108 made of the same material. The material qubit 108 can be a quantum object, such as a trapped ion or neutral atom, which can function as a qubit in a quantum computer or quantum network. The material qubit 108 can function as a single-photon generating material or a single-photon emitter, which generates a single photon in response to electrical or optical excitation of the material qubit 108.

[0056] The matter qubit is placed in an optical cavity to provide parcell enhancement. Parcell enhancement is the effect of increasing the spontaneous emission rate of the matter qubit 108 in response to the matter qubit 108 interacting with the optical cavity 106. This effect also results in an increase in the efficiency of quantum entanglement dispersion of entangled particles.

[0057] Each optical cavity 106 is connected to an actuator 110, such as a piezoelectric transducer. The actuator 110 may be used to actuate a mechanical structure supporting at least a portion of the optical cavity 106 in order to fine-tune the length of the optical cavity 106. One way to detect the amount of adjustment required is to transmit light from an optical light source through the optical cavity 106, and the portion of light from the optical light source 102 that passes through or is reflected from the optical cavity 106 indicates the amount of adjustment required by the actuator 110. The actuator 110 is controlled to maintain a stable length and resonant frequency of the connected optical cavity 106.

[0058] The length of the optical cavity 106 can be adjusted by the actuator 110 so that the optical cavity 106 is in resonance with the transition wavelength of the material qubit 108. The transition wavelength is the wavelength of a single photon captured by the material qubit 108. Therefore, by acting on the mechanical structure supporting the optical cavity 106, the actuator 110 can adjust the length of the optical cavity 106 to lock it to both the optical light source 102 and the transition wavelength of the material qubit 108.

[0059] The optical cavity is in resonance with both the matter qubit 108 and the incident light beam when the light transmitted through the optical cavity 106 is at its maximum value, or when the light reflected by the optical cavity is at its minimum value. The length of the optical cavity 106 can be locked when this criterion is met.

[0060] When the incident light beam 112 is split into multiple light beams 114, and each optical cavity 106 receives one of the light beams 114, each optical cavity 106 of the multiple optical cavities can be locked to the same optical light source 102. That is, one optical light source 102 can be used to lock the lengths of the multiple optical cavities 106 by splitting the incident light beam 112 output by the optical light source 102 before the incident light beam 112 reaches the optical cavities 106. Furthermore, this allows additional components placed before the separation means 104 splits the incident light beam (such as a stable frequency reference or electro-optic modulator) to be used for all or part of the multiple optical cavities, which further reduces the amount of component duplication required when dealing with multiple optical cavities.

[0061] The wavelength (also known as the lock wavelength) of the incident light beam 112 output from the optical light source 102 is selected to be a fixed fraction of the transition wavelength of the matter qubit 108. This is called the fixed-fraction lock optical method.

[0062] Determining the wavelength of the incident light beam 112 using a fixed-fraction locking light method ensures that there is at least one optical cavity length for which the optical cavity 106 is in resonance with both the incident light beam 112 and the transition wavelength of the material qubit 108. That is, this selection of the locking wavelength ensures that the optical cavity 106 can satisfy the double resonance condition of being in resonance with both the incident light beam 112 and the transition wavelength of the material qubit.

[0063] Furthermore, the locking wavelength can be selected such that λ l = λ q * a / b, where a < N, λ q is the fixed transition wavelength of the material qubit 108, λ l is the wavelength of the incident light beam 112, N = z / λ q and N is a number greater than 1 (not necessarily an integer), z is the movement range of the actuator 110, and a and b are integers, and a / b is a simplified fraction. The fraction a / b is the fixed fraction referred to by the term "fixed-fraction locking light" because the fixed wavelength is this fixed fraction of the transition wavelength of the material qubit 108.

[0064] This selection of the lock wavelength ensures that the double resonance condition can be met within the movement range z of the actuator 110. If the wavelength of the incident light beam does not satisfy this requirement and an arbitrary wavelength is selected instead, only a single optical cavity length that satisfies the double resonance condition is guaranteed, and this is only if an offset lock or similar is used to slightly adjust any wavelength (adjustment by at most one free spectral range). Without an offset lock, there may be no optical cavity length that satisfies the double resonance condition. Then, in order to stabilize the lengths of multiple optical cavities using the same optical light source 102, all optical cavities must initially be the same length, at least within the adjustment range of the actuator. Therefore, selecting the wavelength of the incident light beam 112 that satisfies this condition and is a fixed ratio of the transition wavelength of the material qubit 108 ensures that there is at least one point within the movement range of the actuator 110 such that the double resonance condition is met for all optical cavities 106.

[0065] Ideally, the fraction a / b should be as simple as possible, because the more complex the fraction a / b, the larger the range of motion z of the actuator needs to be to ensure that the double resonance condition is met. For example, if the wavelength of the incident light beam 112 is selected to be 17 / 29 of the transition wavelength of the material qubit 108, the range of motion of the actuator needs to be larger than if the range of motion of the incident light beam 112 is selected to be 1 / 3 of the transition wavelength of the material qubit 108. This is to ensure that the double resonance condition is met within the range of motion of the actuator 110, since 17 / 29 is a more complex fraction than 1 / 3. Thus, a and b can be two integers less than 10, or two numbers less than 5. The fraction a / b can be 1 / 2, 2 / 3, 3 / 4, 4 / 5, 2 / 1, 3 / 2, 4 / 3, or 5 / 4. As can be seen, the wavelength of the incident light beam 112 (or lock light) can be greater than or less than the transition wavelength of the material qubit.

[0066] By selecting a fixed fractional lock wavelength for the incident light beam 112 in this way, it becomes possible to provide multiple lockable optical cavities while allowing the required optical cavity length machining tolerance for each optical cavity to be wider than the corresponding actuator travel range. This is useful for the geometric shape of optical cavity 106 where the absolute value of the cavity length is noncritical, or for a nearly confocal geometric shape.

[0067] In practice, for example, due to thermal expansion of the holder of the optical cavity 106, it may be difficult to reliably stabilize or lock the length of the optical cavity when the cavity is at either end of the actuator's travel range. Therefore, it may be desirable to further restrict the value a / N so that the dual resonance point of the optical cavity is not provided at either or near the extreme ends of the actuator's travel range. The exact constraint of a / N required to prevent the dual resonance point of the optical cavity from being very close to the extreme ends of the actuator's travel range, which may impair the stability of cavity locking, will vary depending on factors such as the exact materials and equipment selected in the apparatus setup. For example, if the material of the optical cavity holder is less resistant to thermal expansion compared to a material that is susceptible to thermal expansion, a / N may not need to be as constrained.

[0068] Figure 2 shows another schematic diagram of a device 200 for locking multiple optical cavities according to an aspect of the present disclosure. For simplicity, the separation means 104 is shown to output only a single light beam 114 to a single optical cavity 106. However, it should be understood that, as shown in Figure 1, the separation means 104 can split the light beam reaching the separation means into multiple light beams 114 that can be used to lock multiple optical cavities 106.

[0069] In addition to the components shown and described with respect to apparatus 100 in Figure 1, apparatus 200 may further comprise an electro-optic modulator 202 (EOM) positioned between the optical light source 102 and the separation means 104. The EOM may include lithium niobate or an MgO:LN type crystal. The EOM is a device capable of modulating an incident light beam 112, which may include modulation characteristics including intensity, phase, amplitude, or polarization.

[0070] EOM202 is configured to apply a phase shift to modulate the phase or frequency of the incident light beam 112, thereby enabling the optical cavity 106 to be locked, for example, using a pound-drever-hall (PDH) method. The disclosure is not limited to the PDH method, and the length of the optical cavity 106 may be locked using any suitable cavity locking technique, such as side-of and dither setups.

[0071] The PDH method uses phase-modulated light from an optical light source 102, received within the optical cavity 106. The phase of a portion of the light from the optical light source 102, transmitted through or reflected from the optical cavity 106, is detected, for example, by homodyne detection and compared with the stable wavelength of the optical light source 102 to determine the error and resonant wavelength of the optical cavity 106. The detected error is used to feed back to the actuator 110 to correct the length of the optical cavity 106 so that it is again in resonance with the optical light source 102. Thus, the PDH technique enables the locking of the optical cavity 106 to the optical light source 102 and allows for the measurement of small changes in the length of the optical cavity 106 with very high precision. Any small change in the length of the optical cavity 106 causes the optical cavity 106 to drift from resonance with the stable wavelength of light from the optical light source 102, and thus causes a change, for example, an increase, in the phase error signal detected from the light output from the optical cavity 106 by homodyne detection. By detecting the phase error of the light output from the optical cavity 106, small changes in the length of the optical cavity 106 can be detected. Based on this, the actuator 110 can adjust the length of the optical cavity 106 to compensate for the small changes, so that the optical cavity 106 is in a resonant state with the optical light source 102, which is known as locking the optical cavity 106 to the optical light source 102.

[0072] The limiting factor for the number of optical cavities that can be locked in this way is the amount of light required by each optical cavity. The more light beams 114 into which the incident light beam 112 is split, the lower the intensity of each light beam 114. If too little light reaches the optical cavity, the signal-to-noise ratio of the signal measuring how far the cavity length is from resonance decreases. This reduces the reliability and robustness of locking the optical cavity length.

[0073] Another limiting factor is the maximum transmittance power of the EOM202, which limits the amount of light that can be output from a single EOM202. As mentioned above, if too little light reaches the optical cavity 106, the stability of the lock of the optical cavity 106 decreases.

[0074] Because it depends on the specific optical cavities 106, EOM202, and optical light source 102 selected for the setup, there is no precise number for the maximum number of optical cavities that can be locked in this way.

[0075] Multiple EOMs can be used if the number of optical cavities 106 to be locked is greater than the number that can be reliably locked using a single EOM at its maximum transmitted power. Since optical light sources such as lasers typically have less power output than the EOMs, the incident light beam 112 from the optical light source 102 can be split using the second separation means 204 and transmitted through multiple EOMs 202. For simplicity, Figure 2 shows only one light beam output to a single EOM 202 by the second separation means 204. However, it should be understood that two or more light beams can be output by the second separation means 204, and each of the output light beams is directed to a separate EOM 202, the corresponding setup of which includes multiple optical cavities 106.

[0076] For example, in a device 200 that allows each EOM 202 to lock four optical cavities 106, and a second separation means 204 to allow an incident light beam 112 from an optical light source 102 to pass through three EOMs, a total of 12 optical cavities could then be locked using a single optical light source 102. This is merely illustrative, and the disclosure is not intended to be limited to these numbers.

[0077] Furthermore, depending on the specific EOM202 selected, each EOM202 may enable locking a different number of optical cavities 106. That is, one EOM202 may be capable of locking up to five optical cavities 106, while another EOM202 may be capable of locking up to four optical cavities 106, and yet another EOM202 may be capable of locking up to six optical cavities 106. This is also merely illustrative, and the disclosure is not intended to be limited to these numbers.

[0078] The device 200 may further comprise measuring means 206 for measuring the amount or percentage of light transmitted or reflected from a corresponding optical cavity 106. Measuring means 206 may include a photodetector, such as a coherent detector, configured to detect light transmitted through or reflected from the optical cavity 106. Measuring means 206 may provide a feedback signal to a controller 208, the feedback signal corresponding to the light transmitted or reflected by the optical cavity 106. The feedback signal may be based on the phase of the light output from the optical cavity 106. Measuring means 206 may generate a feedback signal by mixing the detected light signal with a modulated signal from an RF driver and by using homodyne detection to indicate a phase error and reveal the phase difference to be used as a feedback signal.

[0079] The controller 208 may use the received feedback signal to determine the required length and direction of adjustment of the optical cavity 106, and output an error signal to the actuator 110 to control the actuator 110 to adjust the length of the optical cavity 106 and lock the optical cavity 106 to the optical light source 102. The controller 208 may be a feedback controller such as a PID controller.

[0080] The apparatus 200 may further include stabilization means 210 for stabilizing the wavelength of the incident light beam 112 output by the optical light source 102. The stabilization means 210 may generate light at a specific wavelength using a stable reference at the material qubit transition wavelength. A second harmonic generator may be used to generate light for locking the optical light source.

[0081] Furthermore, when the wavelength of the incident light beam 112 is selected according to a fixed fractional lock wavelength method, and light at the transition wavelength of the material qubit 108 can be easily generated, the locked light (or incident light beam 112) can be directly generated without requiring any form of optical light source offset lock using a second harmonic generator or similar (e.g., a third harmonic generator). For example, if the material qubit 108 in the optical cavity contains an alkali element, the vapor cell can provide the exact material qubit transition wavelength as a reference. The frequency of the material qubit transition wavelength can then be doubled, for example, to generate the required frequency of the locked light.

[0082] The apparatus 200 may also include scanning means 212, such as a scanner for scanning the actuator. The scanner can be used to identify resonance points where both the optical cavity and the material qubit are in a resonant state.

[0083] Figure 3 shows the incident light beam at wavelength 112 (Lock) λ. l and single photon emitter wavelength λ e In both cases, the ratio λ is 1:2 e :λ l This shows the transmission of light through the optical cavity 106. In this case, a single photon emitter is provided in the optical cavity 106 instead of the material qubit 108, but those skilled in the art will understand that these components are interchangeable and that the same principles apply regardless of whether the material in the optical cavity is used as the single photon emitter material or as the material qubit 108. In fact, often the single photon emitter and the material qubit are the same material. Therefore, the methods and principles described in this figure in relation to the single photon emitter (e.g., a solid emitter such as nanodiamond, quantum dot, or hexagonal boron nitride) are equally applicable to the material qubit 108 of this disclosure.

[0084] In this particular example, the material within the optical cavity 106 contains neutral atomic rubidium (Rb) 87 with a D2-line transition occurring at 780 nm. A 1:2 emitter-to-lock wavelength ratio is selected so that a standard 1560 nm telecommunications laser can be used as the optical light source 102 to stabilize the length of the optical cavity 106.

[0085] Figure 3 shows the resonance points for both the 780 nm Rb light and the incident light beam 112 output from the laser, where the incident light beam 112 has twice the wavelength of the Rb cell. Since the wavelength of the lock light is twice the wavelength of the Rb emitter, every lock light resonance has a corresponding emitter resonance. Because resonance occurs every integer half wavelength, there are viable double-resonance lock points every 780 nm. That is, the double-resonance condition in which the optical cavity 106 is in resonance simultaneously with both the light from the optical light source 102 and the emission from the Rb cell is met every 780 nm. These points are shown in Figure 3. These lock points are within the range of movement of a standard piezoelectric actuator 110 of a few microns, and therefore all of the optical cavities 106 can be stabilized using the same reference light source and optical light source 102.

[0086] To ensure that the wavelength of the incident light beam 112 emitted by the laser is exactly twice the selected Rb transition wavelength, the laser can be stabilized by referencing a separate Rb cell.

[0087] A second harmonic generator (SHG) can be used to generate light at 780 nm, which is the D2 transition wavelength of Rb. A portion of the light output from the laser is separated using another separation means, such as an optical splitter, and passes through the SHG. The light is then emitted from the SHG at 780 nm and absorbed by the vapor in the Rb cell when it is at or near the atomic resonance of the cell. This can then be used as a reference for stabilizing the laser using saturated absorption spectroscopy locking.

[0088] There are many ways to provide the modulation necessary to lock a laser. For example, a piezoelectric actuator placed within the laser can be used for dithering. Alternatively, atoms can be modulated directly by winding a coil around an Rb cell and adjusting it. Alternatively, an EOM can be provided before a separation means that separates a portion of the light from the laser to the SHG, so that the same EOM can lock both the laser and the optical cavity length.

[0089] Figure 4 shows a method 400 for locking the lengths of multiple optical cavities 106 according to one embodiment of the present invention. Method 400 can be carried out by the apparatus 100 of Figure 1 or the apparatus 200 of Figure 2. The method can be carried out while the apparatus is in use.

[0090] The method includes outputting an incident light beam 112 by an optical light source 102 402. The method further includes receiving the incident light beam output from the optical light source 102 in a separation means 104 404. The method additionally includes splitting the received incident light beam by the separation means 104 to output two or more light beams 114 408. The method further includes receiving one of the light beams 114 transmitted or output from the separation means 104 in each of the plurality of optical cavities 106 408. Each of the plurality of optical cavities includes a matter qubit 108 configured to capture photons and disperse quantum entanglement, the rate of entanglement being increased by the Purcell effect. The type of matter qubit 108 is the same for each of the optical cavities 106.

[0091] The method further includes transmitting or reflecting a portion of light through each of the multiple optical cavities 106 to indicate whether the optical cavities are in a resonant state with the optical light source 102 410. The method may also include measuring a portion of the light transmitted through or reflected from the optical cavities using measuring means 206.

[0092] The method further includes adjusting the length of a corresponding optical cavity 106 based on a portion of the light transmitted through or reflected from the optical cavity 106, using each of a plurality of actuators 110 connected to the corresponding optical cavity 106, so that the optical cavity is in a resonant state with the optical light source 102.412 This may be achieved using measuring means 206 for providing a feedback signal to a controller 208, the feedback signal corresponding to the light transmitted or reflected by the optical cavity 106. The adjustment of the length of the optical cavity 106 may further include a controller 208 for determining the amount and direction of adjustment of the optical cavity 106 using the received feedback signal. The adjustment of the length of the optical cavity may also include the controller 208 outputting an error signal to the actuator 110 to control the actuator 110 to adjust the length of the optical cavity 106 and lock the optical cavity 106 to the optical light source 102. Next, a single photon can be received by or emitted from a matter qubit in order to disperse quantum entanglement.414

[0093] For each optical cavity 106, the incident light beam 112 output from the optical light source 102 is detuned from the transition wavelength of the material qubit 108 by the ratio of two integers a and b, where a / b represents a fixed fraction, to ensure that there is at least one point within the range of movement of the actuator 110 where the double resonance condition is satisfied. When the double resonance condition is satisfied, the optical cavity resonates simultaneously with both the material qubit 108 and the incident light beam 112.

[0094] In particular, the wavelength of the incident light beam 112 is λ l =λ q * may be selected such that a / b, where a <Nであり、λ q λ is the fixed transition wavelength of the matter qubit 108. l This is the wavelength of the incident light beam 112, where N = z / λ q In this equation, N is a number greater than 1 and is not necessarily an integer, and z is the range of motion of the actuator 110.

[0095] Figure 5 shows an exemplary system illustrating how the device can be scaled up to allow for the simultaneous locking of a larger number of optical cavities 106. As mentioned above, one of the limiting factors for the number of optical cavities that can be locked using the same optical light source 102 is the amount of light that can be output by a single EOM 202. One way to overcome this limitation is to provide a second separation means 204 between the optical light source 102 and the EOM 202, allowing the incident light beam 112 output from the optical light source 102 to be sent to multiple EOMs, each of which can be used to lock multiple optical cavities 106. The number of optical cavities 106 that can then be locked is limited by the maximum output power of the optical light source 102.

[0096] One way to scale the setup to lock even more optical cavities is to use multiple optical light sources. Using a single stable reference optical light source 502, such as a laser, multiple smaller and less expensive optical light sources 102 can be offset-locked relative to the reference optical light source 502.

[0097] A reference incident light beam 506 at a desired wavelength is output by a reference optical light source 502 and received by a reference separation means 504. The reference separation means 504 divides or splits the reference incident light beam 506 into a plurality of reference light beams 508. The reference light beams 508 can then be used to lock each optical light source 102 of the setup of the plurality of devices 200.

[0098] Figure 5 shows a reference incident light beam 506 split into two reference light beams 508, which are then sent to two setups of apparatus 200. However, this is merely illustrative, and to keep Figure 5 clear, two setups of apparatus 200 are selected in this case. It should be understood that the reference incident light beam 506 can be split into any number of reference light beams 508, each of which can be transmitted to the setup of apparatus 200 that locks the optical light source 102 of the setup of apparatus 200.

[0099] For example, if each device 200 is enabled to lock 12 optical cavities using a single optical light source 102, and a reference isolation means 504 is enabled to lock 5 of the optical light sources 102 using light from the reference optical light source 502, then a total of 60 optical cavities 108 can be locked using a single reference optical light source 502. This is merely illustrative, and the disclosure is not intended to be limited to these numbers.

[0100] If the maximum transmission power of the reference optical light source 502 is reached and more optical cavities still need to be locked, the system can be further scaled up by daisy-chaining more reference optical light sources 502 together. For example, a light beam could be output from a more powerful optical light source and split into multiple light beams used to stabilize multiple reference optical light sources 502 using additional separation means. This is just one example, and those skilled in the art will recognize that there are many ways in which the apparatus can be further scaled. Alternative approaches may include, for example, using optical transmission cavity locking, multipath atomic reference cells, or alternative designs to optimally utilize a single stable reference.

[0101] The apparatus described with reference to Figures 1-5 functions best under ideal or near-ideal conditions. This assumes that both the wavelength of the lock light from the optical light source 102 and the wavelength of the qubit 108 are reflected from the mirror in the optical cavity in the same manner. In reality, this can be difficult to achieve for several reasons. For example, because the optical coating on the mirror has an inherent penetration depth, the wavelength of the lock light and the wavelength of the material qubit may penetrate different distances within the optical coating. Furthermore, when light is reflected from a curved surface, the light may experience a phase shift.

[0102] These effects can cause the effective cavity length experienced at the lock light wavelength to differ from that at the material qubit wavelength, potentially leading to imperfections at fixed fractional resonance positions. When this occurs, cavity resonance may no longer occur at exactly half-integer multiples of the wavelength.

[0103] The apparatus shown in Figures 1 to 5 yields best results when a custom coating that compensates for the effects described above is used on the optical cavity mirror, and when the optical cavity mirror is manufactured within very tight tolerances.

[0104] Figure 6 is a schematic diagram of a device 600 for locking a plurality of optical cavities according to an aspect of the present disclosure.

[0105] The apparatus 600 comprises an optical light source 102, a separation means 104, a plurality of optical cavities 106, and an actuator 110. For clarity, only one optical cavity 106 is shown in Figure 6, but those skilled in the art will readily understand that any number of optical cavities 106 may be provided. Each optical cavity contains a matter qubit 108.

[0106] The apparatus 600 further comprises a modulator 602 provided between the separation means 104 and the optical cavity 106. Each of the multiple optical cavities is provided with a modulator 602 between the optical cavity and the separation means.

[0107] Each modulator 602 is configured to apply a phase shift to the incident light beam 112 output by the optical light source, thereby modulating the phase and frequency of the incident light beam 112, enabling locking of the optical cavity 106 using, for example, the Pond-Dreber-Hall (PDH) method. Therefore, since modulators 602 can perform the functions described in relation to EOM202, a detailed description of them is not repeated. Each modulator 602 of the plurality of modulators 602 can modulate the phase and frequency of the incident light beam by the same amount, enabling locking of the corresponding optical cavity 106.

[0108] Modulator 602 is also configured to fine-tune the frequency of the incident light beam by applying a small additional frequency shift to the modulated incident light beam. Since each optical cavity may have slightly different mirror curvatures with different optical coating characteristics due to manufacturing tolerances, the amount of the small additional frequency shift required for each optical cavity may vary. Therefore, each modulator 602 of a group of modulators 602 may apply different small additional frequency shifts to the modulated incident light beam so that each optical cavity is individually calibrated for locking.

[0109] The apparatus 600 may further comprise additional components, such as one or more of the components described in relation to Figure 2.

[0110] Figure 7 is a schematic diagram of another apparatus 700 for locking a plurality of optical cavities according to an aspect of the present disclosure.

[0111] The apparatus 700 comprises a first modulator 702 and a second modulator 704. Each of the multiple optical cavities is provided with the first modulator 702 between the optical cavity and the separation means 104. The second modulator 704 is provided between the optical light source 102 and the separation means 104.

[0112] The second modulator 704 may be an EOM. The second modulator 704 may be an EOM202. Since the second modulator 704 modulates the incident light beam 112 for each of the multiple optical cavities 106, the second modulator 704 effectively acts on all of the optical cavities 106 that receive the light beam via the separation means 104.

[0113] The first modulator 702 may be an EOM or an acousto-optic modulator. The first modulator 702 further modulates the modulated incident light beam from the second modulator 704. This provides a small additional frequency shift to account for the non-uniformity of the optical cavities. Each of the first modulators 702 may apply a different frequency shift so that each optical cavity is individually optimized for locking.

[0114] The adjustability required to compensate for the effects of tolerances on optical coatings and other manufacturing tolerances is significantly lower than the adjustability required to account for other effects shared between cavities to ensure that the double resonance condition is met. Thus, the second modulator 704 can perform greater modulation than the first modulator 702.

[0115] For both apparatus 600 and apparatus 700, the incident light beam output from the optical light source 102 is tuned to approach the correct wavelength for the optical cavity. The correct wavelength is close to a fixed fractional wavelength, which undergoes a small amount of detuning to optimize the penetration depth and radius of curvature effects. Then, a small additional frequency shift is applied for each cavity using a fine frequency shift element to account for residual shift and manufacturing tolerances. The first broad frequency shift can be provided by the second modulator 704 (as shown in apparatus 700) or by direct adjustment of the frequency of the reference light (e.g., using a frequency comb).

[0116] The second modulator 704 may be an EOM with an adjustment range of approximately 10 GHz. The first modulator 702 may be an EOM or an acousto-optic modulator. A typical acousto-optic modulator has an adjustment range of approximately 0.1 GHz.

[0117] While a first modulator 702 is required for each optical cavity, a second modulator 704 may be used for multiple optical cavities; therefore, to reduce the overall cost of the apparatus 700, it may be desirable to use a less expensive modulator as the first modulator 702. Since AOMs tend to be less expensive than EOMs, the first modulator may preferably be an AOM. If both the first modulator 702 and the second modulator 704 are EOMs, the first modulator may be a lower quality or less expensive EOM than the second modulator 704. The tunability required to ensure that the double resonance condition is met is greater than the tunability provided by a typical AOM. Therefore, an AOM is typically not a suitable choice for the second modulator 704.

Claims

1. A device for stabilizing the lengths of multiple optical cavities, wherein the device is An optical light source configured to output an incident light beam, A separation means configured to receive the incident light beam output from an optical source, and to split the received incident light beam, thereby outputting two or more light beams, It comprises a plurality of optical cavities, and each of the plurality of optical cavities is One of the light beams output from the separation means is received, The optical cavity transmits or reflects a portion of the light that indicates whether it is in a resonant state with the optical light source. To lock the optical cavity to the optical source, it is connected to an actuator configured to adjust the length of the optical cavity based on a portion of the light that has passed through or been reflected from the optical cavity, so as to be in a resonant state with the optical source, The optical cavity is configured to house a material qubit, and the material qubit is configured to capture photons and disperse quantum entanglement, and the speed of entanglement is increased by the Purcell effect. The aforementioned material qubit is the same for each optical cavity, A device wherein, for each optical cavity, the incident light beam is detuned from the transition wavelength of the material qubit by a ratio of two integers a and b, where a / b represents a fixed fraction, so as to ensure that there is at least one point within the range of movement of the actuator where a double resonance condition is satisfied, such that the optical cavity resonates simultaneously with the material qubit and the incident light beam.

2. The apparatus according to claim 1, further comprising a first modulator disposed between the separation means and the optical cavity for each of the plurality of optical cavities.

3. The apparatus according to claim 2, wherein the first modulator is an electro-optic modulator, EOM, or an acousto-optic modulator, AOM.

4. The apparatus according to any one of claims 1 to 3, further comprising a second modulator disposed between the optical light source and the separation means for applying a phase shift to the incident light beam, wherein the second modulator is an electro-optic modulator.

5. The apparatus according to claim 4, further comprising a second separation means disposed between the optical light source and the second modulator for dividing the incident light beam into a plurality of incident light beams.

6. The apparatus according to any one of claims 1 to 5, further comprising measuring means for measuring the proportion of light transmitted through or reflected from each optical cavity.

7. The apparatus according to any one of claims 1 to 6, further comprising scanning means for scanning each actuator.

8. The wavelength of the incident light beam is λ ｌ = λ ｑ * Selected such that a / b, where a < N, In the formula, λ ｑ However, the transition wavelength of the material qubit is fixed, and λ ｌ However, this is the wavelength of the incident light beam, where N = z / λ ｑ The apparatus according to any one of claims 1 to 7, wherein in the formula, N is a number greater than 1 and is not necessarily an integer, z is the range of movement of the actuator, a and b are integers as described in claim 1, and a / b is a simplified fraction.

9. The apparatus according to any one of claims 1 to 8, wherein a and b are 10 or less, and optionally a and b are 5 or less.

10. The apparatus according to claim 9, wherein the ratio of the wavelength of the incident light beam to the wavelength of the material qubit is 1:2, 2:3, 3:4, 4:5, 2:1, 3:2, 4:3, or 5:

4.

11. The apparatus according to any one of claims 1 to 10, wherein the wavelength of the incident light beam is in the range of 600 to 1600 nm.

12. The apparatus according to any one of claims 1 to 11, wherein the separation means is an optical splitter.

13. The apparatus according to any one of claims 1 to 12, wherein the material qubit comprises a neutral atom or a trapped ion.

14. The apparatus according to any one of claims 1 to 13, wherein the actuator is a piezo actuator.

15. The apparatus according to any one of claims 1 to 14, wherein the optical light source is a laser.

16. The apparatus according to any one of claims 1 to 15, wherein each of the optical cavities includes a double-band coating.

17. The apparatus according to any one of claims 1 to 16, further comprising a locking means for stabilizing the length of each of the optical cavities.

18. The apparatus according to any one of claims 1 to 17, wherein the actuator is configured to lock each of the optical cavities into a resonant state with the optical light source using pound-drever-hole technology, side-of-peak lock technology, or dither-lock technology.

19. The apparatus according to any one of claims 1 to 18 for use in quantum computing and / or quantum networking applications.

20. The apparatus according to any one of claims 1 to 19, further comprising stabilization means for stabilizing the optical light source.

21. The apparatus according to claim 20, wherein the stabilization means generates fixed-fraction lock light at a fixed-fraction wavelength using a reference that is stable at the qubit transition wavelength.

22. The apparatus according to claim 21, further comprising a second harmonic generator or optical transmission cavity for generating the fixed fraction lock light.

23. The apparatus according to any one of claims 20 to 22, wherein the optical light source is stabilized by reference to an atomic vapor cell or an optical frequency comb.

24. The apparatus according to claim 23, wherein the optical light source is stabilized with reference to a HeNe laser, or the atomic vapor cell includes an Rb cell.

25. A system for stabilizing the lengths of multiple optical cavities, wherein the system At least two devices according to any one of claims 1 to 19, A reference optical source configured to output a reference incident light beam, The system includes a reference separation means configured to receive the reference incident light beam output from the reference optical source and to split the received reference incident light beam into two or more reference light beams, A system in which each optical light source of at least two of the aforementioned devices is stabilized with reference to one of the output reference light beams.

26. A method for stabilizing the lengths of multiple optical cavities, wherein the method is The process involves outputting an incident light beam using an optical light source, In the separation means, receiving the incident light beam output from the optical source, The separation means divides the received incident light beam so as to output two or more light beams, For each of the multiple optical cavities, Receiving one of the light beams output from the separation means, The optical cavity transmits or reflects a portion of the light indicating whether it is in a resonant state with the optical light source, An actuator connected to the optical cavity adjusts the length of the optical cavity based on the portion of light that has passed through or been reflected from the optical cavity so as to be in a resonant state with the optical source, in order to lock the optical cavity to the optical source. This method involves capturing photons with a material qubit located within the optical cavity to disperse quantum entanglement, wherein the entanglement rate is increased by the Purcell effect. The aforementioned material qubit is the same for each optical cavity, A method in which, for each optical cavity, the incident light beam is detuned from the transition wavelength of the material qubit by a ratio of two integers a and b, where a / b represents a fixed fraction, so as to ensure that there is at least one point within the range of movement of the actuator where a double resonance condition is satisfied, such that the optical cavity resonates simultaneously with the material qubit and the incident light beam.

27. For each optical cavity, The method according to claim 26, further comprising measuring the portion of light by means of a measuring means to determine the proportion of light that has passed through or been reflected from the optical cavity.

28. The method according to claim 27, further comprising locking the length of the optical cavity by a locking means when the determined proportion of transmitted or reflected light is within a predetermined range.

29. The method according to claim 28, wherein the length of the optical cavity is locked when the determined proportion of transmitted light is at its maximum or the determined proportion of reflected light is at its minimum.

30. The method according to claim 28 or 29, wherein the optical cavity is locked using a pound-drever hole technique, a side-of-peak lock technique, or a dither lock technique.

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