WO2023073344A1

WO2023073344A1 - Quantum random number generation

Info

Publication number: WO2023073344A1
Application number: PCT/GB2022/052625
Authority: WO
Inventors: Joanna ZAJAC; Jason Smith
Original assignee: Oxford University Innovation Limited
Priority date: 2021-11-01
Filing date: 2022-10-14
Publication date: 2023-05-04
Also published as: GB202115672D0

Abstract

Examples disclosed herein provide a quantum random number generator apparatus comprising: a single photon source configured to undergo resonance fluorescence to generate a stream of single photons; a beam splitter configured to receive the stream of single photons generated at the single photon source and generate, from the stream of single photons, a first photon stream and a second photon stream; a detector module; a first detector electrically connected to the detector module, the first detector configured to receive the first photon stream and generate a first detection signal; a second detector electrically connected to the detector module, the second detector configured to receive the second photon stream and generate a second detection signal; wherein the detector module is configured to receive the first detection signal and the second detection signal and generate a random number from the first and second detection signals.

Description

QUANTUM RANDOM NUMBER GENERATION

Technical Field

[0001] The present disclosure relates to quantum computing and, in particular, quantum random number generation. Examples relate to an apparatus and methods for generating random numbers through quantum random number generation.

Background

[0002] Random numbers are used in a wide variety of applications, including encryption. In many random number applications, it is beneficial for the generated numbers to be truly random, so that a third party, such as a malicious party attempting to intercept an electronic communication, cannot readily predict the outcome of the random number generation and crack the encryption of an encrypted file. Random number generation generated through classical means maintains an element of predictability, because the numbers are generated via a software implementation of a random number generator, which is not a truly random process. A pseudo-random generator algorithm may generate a random number stream, and most digital data processing electronics, such as personal computers and servers, are inherently deterministic, thereby providing a pseudo-random number. A physical random number generator may also be implemented, and these may be classical or quantum. Both of them, however, are based on physical processes, i.e. light detection or current measurements. Only random number generation based on a quantum mechanical process, however, is fundamentally random. Thus, development of random number generators implemented using quantum mechanical effects is currently a field of significant activity.

[0003] Cryptographic systems may be considered to be secure when sufficient entropy is generated by the underlying Entropy Source (ES) within the random number generator (RNG). Security standards, such as NIST SP 800-90B and BSI AIS-31 , use the quality of the ES for benchmarking. There may be considered to be three classes of RNGs. Pseudo-RNGs are based on algorithms, i.e. the Marsanne-Twister algorithm, for generating a random number stream. However, fast algorithms for factorising prime numbers, such as Shor’s algorithm, can reveal the seed and compromise the security of encryption based on this type of RNG. Physical, or True, RNGs (PRNGs / TRNGs) are based on metastable or chaotic (physical) processes. Their quality may consequently be inconsistent, and difficult to access, while their exact state is unknown. PRNGs may also produce low quality randomness that heavily relies on postprocessing. Finally, there are Quantum RNGs (QRNGs). This type offers the highest entropy compared with other classes, and may be able to generate a high quality number stream even without postprocessing. Their operation is based on principles of quantum mechanics, and is thus fundamentally probabilistic, making them more resilient to attack by a malicious party.

[0004] Examples disclosed here set out apparatuses and methods of quantum random number generation.

Summary

[0005] According to an aspect, there is provided a quantum random number generator apparatus comprising: a single photon source configured to undergo resonance fluorescence to generate a stream of single photons; a beam splitter configured to receive the stream of single photons generated at the single photon source and generate, from the stream of single photons, a first photon stream and a second photon stream; a detector module; a first detector electrically connected to the detector module, the first detector configured to receive the first photon stream and generate a first detection signal; a second detector electrically connected to the detector module, the second detector configured to receive the second photon stream and generate a second detection signal; wherein the detector module is configured to receive the first detection signal and the second detection signal and generate a random number from the first and second detection signals.

[0006] The first detector of the quantum random number generator apparatus may be synchronized with the second detector, for the first and second detectors to perform synchronised detection in order to ensure accurate photon counting.

[0007] High emission rates may be achieved using resonance fluorescence compared with other excitation methods, such as photoluminescence.

[0008] The single photon source may exhibit near-unity quantum efficiency, e.g. above 95% quantum efficiency; possibly, above 99% quantum efficiency. The quantum efficiency of an emitter is an intrinsic property of the material used to provide the single photons; i.e. a property of the single photon source.

[0009] The single photon source may comprise a crystal lattice comprising a defect centre. The crystal lattice may comprise one or more of: diamond; silicon nitride; silicon carbide; gallium nitride and boron nitride. The defect centre may comprise: an implanted centre, a laser-written centre, or an intrinsic centre. The defect centre may comprise a trapped vacancy and substitutional atom. The defect centre may be, for example, a silicon vacancy centre; a germanium vacancy centre, or a tin vacancy centre.

[0010] The single photon source may be configured to undergo resonance fluorescence at a temperature between approximately 4K and 300K to generate the stream of single photons, Preferably, the temperature may be between approximately 270K and 300K, i.e. room temperature or ambient temperature.

[0011] The single photon source may be enclosed in a hemisphere. The hemisphere may be a focussed ion beam milled hemisphere. Enclosing the single photon source in a hemisphere may increase the count rate, i.e., the number of generated photons emitted per unit time and thus the efficiency of apparatus.

[0012] The single photon source may be enclosed in an optical resonator. The optical resonator may comprise one or more of: two opposing mirrors, a bullseye, and a photonic crystal structure. Enclosing the single photon source in an optical resonator may increase the count rate, i.e., the number of generated photons emitted per unit time.

[0013] The quantum random number generator apparatus may comprise a laser excitation source configured to cause the single photon source to undergo time-triggered resonance fluorescence to generate the stream of single photons.

[0014] The quantum random number generator apparatus may comprise an laser excitation source configured to excite single photon source emission in the single photon source via resonance fluorescence. The laser excitation source may comprise a continuous-wave laser modulated using an electro-optic modulator.

[0015] An excitation pulse emission rate of the laser excitation source may be up to 500 MHz. The excitation pulse emission rate may be determined, at least in part, by the lifetime of a defect centre in a crystal lattice single photon source. For example, if the single photon source comprises a crystal lattice having a nitrogen vacancy (NV) present as a defect centre, an excitation pulse emission rate of around 500 MHz results from the lifetime of NV centre.

[0016] The laser excitation source may provide photons in a photon antibunching emission scheme. The antibunching characteristics of the laser excitation source may be used to determine that the single photon source is emitting single photons.

[0017] The laser excitation source may be configured to resonantly excite single photon source emission. This may be performed for use in random number generation. In some examples, the laser excitation source may be configured to perform excitation of the single photon source at an energy above the single photon source bandgap, for the purposes of preliminary assessment of the properties of the system.

[0018] The detector module may be configured to allocate a “1” value to a photon received in the first photon stream; and allocate a “1” value to a photon received in the second photon stream. In this way a bitstream may be obtained and used to generate a random number.

[0019] The quantum random number generator apparatus may comprise a post-processing module electrically connected to the detector module. The post-processing module may be configured to receive a detection signal from the detector module, the detection signal representing the first and second detection signals; and perform, on the received detection signal, one or more of beam splitter asymmetry compensation, entropy distillation, and dark count correction.

[0020] According to another aspect, there is provided a quantum random number generation method, comprising: causing a single photon source to undergo resonance fluorescence to generate a stream of single photons; generating, using a beam splitter, a first photon stream and a second photon stream from the stream of single photons; receiving the first photon stream at a first detector to generate a first detection signal from the first photon stream; receiving the second photon stream at a second detector to generate a second detection signal from the second photon stream; receiving the first detection signal and the second detection signal at a detector module; and generating a random number from the first and second detection signals. The photon stream may comprise a photon or an absence of a photon.

[0021] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons may comprise exciting single photon source emission in the single photon source using a continuous-wave laser to cause the single photon source to undergo time-triggered resonance fluorescence. The continuous wave laser may be modulated using an electro-optic modulator.

[0022] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons may comprise exciting single photon source emission in the single photon source at an excitation pulse emission rate of up to 500 MHz, to cause the single photon source to undergo time-triggered resonance fluorescence.

[0023] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons may comprise exciting single photon source emission in the single photon source resonantly to cause the single photon source to undergo time-triggered resonance fluorescence. In some examples, excitation of the single photon source may be performed at an energy above the single photon source bandgap, for the purposes of preliminary assessment of the properties of the system.

[0024] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons may comprise exciting single photon emission from a crystal lattice comprising a defect centre, The crystal lattice may comprise diamond, silicon nitride, silicon carbide, gallium nitride, or boron nitride.

[0025] Exciting single photon emission from the crystal lattice comprising a defect centre may comprise exciting single photon emission from a crystal lattice comprising a defect centre wherein the defect centre comprises a trapped vacancy and substitutional atom. The defect centre may be, for example, a silicon vacancy centre, a germanium vacancy centre, or a tin vacancy centre.

[0026] The method may be performed at a temperature between approximately 4K and 300K. Preferably, the temperature may be between approximately 270K and 300K.

[0027] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons may comprise exciting single photon source emission in a photon antibunching emission scheme.

[0028] The method may comprise synchronising the first detector with the second detector.

[0029] According to another aspect, there is provided a machine-readable medium having program code stored thereon which, when executed by any apparatus disclosed herein, causes the machine to perform any operation or operations disclosed herein.

Brief Description Of The Drawings

[0030] Examples are further described hereinafter with reference to the accompanying drawings, in which:

Figures 1a-1 b illustrate a quantum RNG apparatus according to examples disclosed herein;

Figure 2a shows a single photon source enclosed in a hemisphere according to examples disclosed herein;

Figure 2b shows a single photon source enclosed in an optical resonator according to examples disclosed herein;

Figure 3 shows a method of quantum random number generation according to examples disclosed herein; and

Figure 4 illustrates a controller for use in quantum random number generation according to examples disclosed herein.

[0031] Throughout the description and the drawings, like reference numerals refer to like parts.

Detailed Description

[0032] Cryptographic systems may be considered to be secure when sufficient entropy is generated by the underlying Entropy Source (ES) within the random number generator (RNG). Quantum random number generators (QRNGs) offer the highest entropy compared with other classes of RNG. Their operation is based on principles of quantum mechanics, and is thus fundamentally probabilistic, making them more resilient to attack.

[0033] Figures 1a-1 b illustrate an example quantum RNG apparatus 100. The apparatus 100 comprises a single photon source 102 which is configured to undergo resonance fluorescence (RF) to generate a stream of single photons 103. High emission rates may be achieved using RF compared with other excitation methods, such as photoluminescence. Resonance fluorescence may be thought of as a process in which a two-level atomic system interacts with an electromagnetic field driven at a frequency at or near the natural frequency of the atom. Here we are concerned within the low excitation regime, i.e. wherein the Rabi frequency associated with the excitation source (e.g. the driving laser field) is smaller than the spectral width of the atom. A “two-level” atomic system describes a system in which the atom can be found in the two possible states - either an electron is found in its ground state or the excited state. Typically a monochromatic laser is used to excite the atomic system. Once the atomic system is excited by an incoming photon (e.g. from a laser), it can relax via photon release at the frequency of the absorbed incoming photon. Pulsed RF may be used as an effective way of deterministically generating high quality photons with minimal dephasing. An example method of performing RF is to use a gigahertz-bandwidth electro-optic modulator (EOM) to modulate the output of a tuneable continuous-wave (CW) laser for resonant excitation of a single photon source. The EOM may be driven by a fast programmable electronic pulsepattern generator (PPG). To perform RF, a cross-polarisation technique may be employed in which orthogonally oriented linear polarizers are placed in the excitation and collection arms of the apparatus 100 to suppress resonant excitation laser photons in the collected photon stream 103.

[0034] The apparatus 100 comprises a beam splitter 104 which is configured to receive the stream of single photons 103 generated at the single photon source 102 and generate, from the stream of single photons 103, a first photon stream 105a and a second photon stream 105b. The apparatus 100 also comprises a detector module 108, a first detector 106a electrically connected to the detector module 108, and a second detector 106b electrically connected to the detector module 108. The detectors 106a, 106b may, for example, be homodyne detectors.

[0035] A single photon generated by the single photon source 102 impinges on the beam splitter 104 and may then be detected by one of the two single photon detectors 106a, 106b after travelling along one of the two output photon paths 105a, 105b. Before detection at a detector 106a, 106b, the generated photon is in a quantum mechanical superposition state of the two possible outcomes (either travelling along the first path 105a or travelling along the second path 105b). Upon detection (measurement) at a detector 106a, 106b, the photon position is determined. The detection of photons at the first detector 106a and the second detector 106b may be used to generate a raw random bit stream. This may be performed at the detector module 108.

[0036] The first detector 106a is configured to receive the first photon stream 105a and generate a first detection signal. The second detector 106b is electrically connected to the detector module 108 and is configured to receive the second photon stream 105b and generate a second detection signal. The detector module 108 is configured to receive the first detection signal (as illustrated, via a first connection 107a such as an electrical wire) and the second detection signal (as illustrated, via a second connection 107b such as an electrical wire) and generate a random number from the first and second detection signals. The first detector 106a of the quantum RNG apparatus 100 may be synchronized with the second detector 106b for accurate timing.

[0037] The single photon source 102 may exhibit near-unity quantum efficiency, e.g. above 95% quantum efficiency; possibly, above 99% quantum efficiency. The quantum efficiency is an intrinsic property of the single photon emitter used to provide the single photons.

[0038] The single photon source 102 may comprise a crystal lattice comprising a defect centre (which may also be called a colour centre or an impurity-vacancy centre). The crystal lattice may comprise one or more of, for example: diamond; silicon nitride; silicon carbide; gallium nitride and boron nitride. Other possible crystal lattices may be envisaged by the skilled person. The defect centre may comprise: an implanted centre, a laser-written centre, or an intrinsic centre. Using a laser-written centre may be advantageous in terms of scaling up manufacture of a single photon source formed in this way, because it allows for deterministic positioning of a defect centre such as an nitrogen vacancy (NV) or silicon vacancy (SiV) centre, and may allow for on-chip manufacture at high spatial density of up to 10⁷/cm². The defect centre may comprise a trapped vacancy and substitutional atom. The defect centre may be, for example, a silicon vacancy centre; a germanium vacancy centre, or a tin vacancy centre. Other possible defect centres may be envisaged by the skilled person. In an example, a diamond crystal lattice comprising an NV defect centre may be used. A defect centre such as an NV centre in diamond may provide good overall optical properties such as near-unity quantum efficiency and high photostability.

[0039] Figure 1 b shows, in addition to the elements illustrated in Figure 1a, an excitation source 110 such as a monochromatic laser, configured to excite resonant excitation in the single photon source 102. The laser excitation source 110 may be configured to cause the single photon source 102 to undergo time-triggered resonance fluorescence to generate the stream of single photons 103. The laser excitation source 110 may be configured to excite single photon source emission 103 in the single photon source 102 via resonance fluorescence. The laser excitation source 110 may comprise a continuous-wave laser modulated using an electro-optic modulator in some examples.

[0040] An excitation pulse emission rate of the laser excitation source 110 may be up to 500 MHz in some examples. The excitation pulse emission rate may be determined, at least in part, by the lifetime of a defect centre in the crystal lattice single photon source 102. For example, if the single photon source 102 comprises a crystal lattice having a nitrogen vacancy (NV) present as a defect centre, an excitation pulse emission rate of around 80 MHz results from the lifetime (a natural lifetime of around 13 ns) of NV centre. As another example, a SiV centre, with a shorter lifetime, may have an excitation pulse emission rate of around 500 MHz [0041] The laser excitation source 110 may provide photons in a photon antibunching emission scheme. The antibunching characteristics of the laser excitation source 110 may be used to determine that the single photon source 102 is emitting single photons.

[0042] The laser excitation source 110 may be configured to resonantly excite single photon source emission. This may be performed for use in random number generation. In some examples, the laser excitation source 110 may be configured to perform excitation of the single photon source 102 at an energy above the single photon source bandgap, for the purposes of preliminary assessment of the properties of the system.

[0043] Using time-triggered RF advantageously provides a higher emission rate than photoluminescence; in some cases up to 100 times higher. The rate may be set by the laser modulation frequency used to excite photon emission from the source 102. The emission rate of up to 100x that obtainable using photoluminescence may be so achieved while maintaining desirable single photon emitter characteristics. Photon emission rates before postprocessing of the detected photon stream may be up to 500 Mbit/s, which is a high performance emission rate.

[0044] The single photon source 102 may be configured to undergo resonance fluorescence at a temperature between approximately 4K and 300K to generate the stream of single photons 103. Preferably, the temperature may be between approximately 270K and 300K, i.e. room temperature or ambient temperature. For example, excitation of single photons from a diamond single photon source having a defect centre (e.g. a NV centre) may be excited by an optical source and stably provide single photon streams in room temperature conditions. Other types of QRNG, such as those using inorganic semiconductor quantum dots as a single photon source, typically operate at very low temperatures (i.e. liquid helium temperatures around 4K) and thus require complex refrigeration systems. By permitting operation at room temperature, examples discussed herein provide a simpler QRNG apparatus which may be easier to operate and more readily commercialised (e.g. scalable) than a low temperature system.

[0045] The detector module 108 may be configured to allocate a “1” value to a photon received in the first photon stream 105a; and allocate a “1 ” value to a photon received in the second photon stream 105b. The random number may then be used, for example, as a key to encrypt data prior to data transmission to secure the data from being intercepted.

[0046] Also illustrated is a post-processing module 112 electrically connected to the detector module. The post-processing module 112 may be configured to receive the detected photon stream from the detector module 108 and apply post processing to improve the output signal. The detection signal represents the first and second detection signals corresponding to the first and second photon streams 105a, 105b. The post-processing module 112 may be configured to perform, on the received detection signal, some post-processing, such as beam splitter asymmetry compensation, entropy distillation, and dark count correction. Postprocessing may comprise first characterising the system, then unbiasing any beam-splitter asymmetry. Furthermore, entropy distillation algorithms may be designed and implemented for number stream post-processing.

[0047] Thus, using the photon stream 103 generated by the single photon source 102, and a beam splitter 104 with corresponding detectors 106a, 106b, random numbers may be generated through a “which-way” process taking place at the beam splitter 104. In some examples disclosed herein, a 500 MHz rate may be obtained (e.g. by using resonance fluorescence and an SiV centre in diamond as a single photon source) which is higher than previously demonstrated.

[0048] Figure 2a shows an example single photon source 102 comprising a crystal lattice defect 204 enclosed in a hemisphere 202. The single photon source 102 may be considered to be enclosed in a hemisphere. The hemisphere 202 may be a focussed ion beam milled hemisphere. Enclosing the single photon source 204 in a hemisphere 202 may increase the count rate, i.e., the number of generated photons emitted per unit time, as more photons may be collected by using a hemisphere.

[0049] In this example, the emitter 204 is enclosed by a solid structure comprising a hemisphere 202 on one side of the defect and a distributed Bragg-Reflector (DBR) 206 on the other side. The DBR acts as a mirror, which in this example results from periodic variation in the refractive index in the DBR. In other examples a DBR may result from periodic variation of some other characteristic (such as height of a dielectric waveguide). Each layer boundary in the DBR causes a partial reflection of an optical wave. The DBRs may be coated onto the crystal lattice external surfaces, or onto a separate substrate which is then affixed to the device. The curved surface of the hemisphere may be coated with an antireflection coating 205 to maximise the coupling of photons out of the structure (in the upwards direction on Figure 2a).

[0050] Such a structure 202 may increase the bit rate of the QRNG by increasing the efficiency of single photon coupling through the apparatus. Such a structure 202 may also reduce the power requirements of the device by reducing the optical power needed to perform resonance fluorescence of the single photon emitter. The geometry of such a source 102 may be characterised using a confocal microscope. The emission characteristics of such a source may be characterised using Hanbury, Brown and Twiss (HBT) interferometry, for example using two synchronised single-photon avalanche diodes (SPADs) to assess the auto- correlation function g²(t) of generated photons and determine that single photon emission is taking place.

[0051] Figure 2b shows a single photon source 102 enclosed in an optical resonator 208 according to some examples. An optical resonator may comprise a series of mirrors arranged to form a standing wave cavity resonator for light provided by an excitation source 110. The single photon source may be enclosed in an optical resonator. The optical resonator may comprise one or more of: two opposing mirrors 208, a bullseye, and a photonic crystal structure or any other resonator design. Enclosing the single photon source 102 in an optical resonator may increase the bit rate of the QRNG, by increasing the rate of single photon emission via the modification of the optical density of states (the Purcell effect).

[0052] The quantum-generated random number obtained at the detector 108 may be used, for example, to encrypt data prior to data transmission to secure the data from being intercepted. A cryptographic key may be generated using the quantum-generated random number, and since the random number is truly random, as it is generated via a quantum mechanical process, the encryption is strong and difficult/impossible to break because the key cannot be guessed by an attacker. Neither can the random number generation process can be hacked as it is resilient to external attacks. Encryption may also be strengthened if the key is refreshed (i.e. a new key is generated) regularly, and examples disclosed herein provide high enough yields of random numbers to enable regular key refreshing.

[0053] Figure 3 shows a method 300 of quantum random number generation according to examples disclosed herein. The method 300 comprises: causing a single photon source to undergo resonance fluorescence to generate a stream of single photons 302; generating, using a beam splitter, a first photon stream and a second photon stream from the stream of single photons 304; receiving the first photon stream at a first detector to generate a first detection signal from the first photon stream 306; receiving the second photon stream at a second detector to generate a second detection signal from the second photon stream 308; receiving the first detection signal and the second detection signal at a detector module 310; and generating a random number from the first and second detection signals 312. The photon stream may comprise a photon or an absence of a photon.

[0054] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons 302 may comprise exciting single photon source emission in the single photon source using a continuous-wave laser to cause the single photon source to undergo time-triggered resonance fluorescence. The continuous wave laser may be modulated using an electro-optic modulator.

[0055] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons 302 may comprise exciting single photon source emission in the single photon source at an excitation pulse emission rate of up to 500 MHz, to cause the single photon source to undergo time-triggered resonance fluorescence.

[0056] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons 302 may comprise exciting single photon source emission in the single photon source resonantly to cause the single photon source to undergo time-triggered resonance fluorescence. In some examples, excitation of the single photon source may be performed at an energy above the single photon source bandgap, for the purposes of preliminary assessment of the properties of the system.

[0057] Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons 302 may comprise exciting single photon emission from a crystal lattice comprising a defect centre, The crystal lattice may comprise diamond, silicon nitride, silicon carbide, gallium nitride, or boron nitride. Exciting single photon emission from the crystal lattice comprising a defect centre may comprise exciting single photon emission from a crystal lattice comprising a defect centre wherein the defect centre comprises a trapped vacancy and substitutional atom. The defect centre may be a silicon vacancy centre, a germanium vacancy centre, or a tin vacancy centre.

[0058] The method may be performed at a temperature between approximately 4K and 300K. Preferably, the temperature may be between approximately 270K and 300K. Causing the single photon source to undergo resonance fluorescence to generate a stream of single photons 302 may comprise exciting single photon source emission in a photon antibunching emission scheme. The method 300 may comprise synchronising the first detector with the second detector in some examples.

[0059] Figure 4 illustrates a controller 400 for use in quantum random number generation according to some examples disclosed herein. The controller 400 in this example comprises at least one processor 402 and a memory 404 connected to the at least one processor 402. The memory 404 may be considered an example of a machine-readable medium having program code stored thereon. The program code (software) may, when executed by the processor 402 in communication with elements of any apparatus 100 disclosed herein (e.g. the excitation source 110 or a controller thereof; the detector 108 or a controller thereof, the post-processing module 112 or a controller thereof), cause the processor 402 to perform any operation or operations disclosed herein. Such program code may be stored in the form of volatile or non-volatile storage 404 such as on a storage device. Such a storage device may be a ROM, RAM, chip memory, a memory device, integrated circuit memory, or an optically or magnetically readable medium such as CD, DVD, or magnetic disk or tape. Computer program code as disclosed herein may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and examples suitably encompass the same.

[0060] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example of a generic series of equivalent or similar features. Many modifications and other examples set out herein will come to mind to a person skilled in the art in light of the teachings presented herein. Therefore, it will be understood that the disclosure herein is not to be limited to the specific examples disclosed herein. Moreover, although the description provided herein provides examples in the context of certain combinations of elements, steps and/or functions may be provided by alternative examples without departing from the scope of the appended claims.

Claims

1 . A quantum random number generator apparatus comprising: a single photon source configured to undergo resonance fluorescence to generate a stream of single photons; a beam splitter configured to receive the stream of single photons generated at the single photon source and generate, from the stream of single photons, a first photon stream and a second photon stream; a detector module; a first detector electrically connected to the detector module, the first detector configured to receive the first photon stream and generate a first detection signal; a second detector electrically connected to the detector module, the second detector configured to receive the second photon stream and generate a second detection signal; wherein the detector module is configured to receive the first detection signal and the second detection signal and generate a random number from the first and second detection signals.

2. The quantum random number generator apparatus of any preceding claim, wherein the single photon source comprises a crystal lattice comprising a defect centre.

3. The quantum random number generator apparatus of claim 2 or claim 3, wherein: the crystal lattice comprises one or more of: diamond; silicon nitride; silicon carbide; gallium nitride and boron nitride.

4. The quantum random number generator apparatus of claim 3 or claim 4, wherein the defect centre comprises: an implanted centre, a laser-written centre, or an intrinsic centre.

5. The quantum random number generator apparatus of any of claims 2 to 4, wherein the defect centre comprises a trapped vacancy and substitutional atom; optionally, wherein the defect centre is a silicon vacancy centre; a germanium vacancy centre, or a tin vacancy centre.

6. The quantum random number generator apparatus of any preceding claim, wherein the single photon source is configured to undergo resonance fluorescence at a temperature between approximately 4K and 300K to generate the stream of single photons; preferably, wherein the temperature is between approximately 270K and 300K.

7. The quantum random number generator apparatus of any preceding claim, wherein the single photon source is enclosed in a hemisphere; optionally, wherein the hemisphere is a focussed ion beam milled hemisphere.

8. The quantum random number generator apparatus of any preceding claim, wherein the single photon source is enclosed in an optical resonator; optionally, wherein the optical resonator comprises one or more of: two opposing mirrors, a bullseye, and a photonic crystal structure.

9. The quantum random number generator apparatus of any preceding claim, comprising a laser excitation source configured to cause the single photon source to undergo time- triggered resonance fluorescence to generate the stream of single photons.

10. The quantum random number generator apparatus of any preceding claim; comprising an laser excitation source configured to excite single photon source emission in the single photon source via resonance fluorescence; optionally, wherein the laser excitation source comprises a continuous-wave laser modulated using an electro-optic modulator.

11 . The quantum random number generator apparatus of claim 11 ; wherein an excitation pulse emission rate of the laser excitation source is up to 500 MHz.

12. The quantum random number generator apparatus of any of claims 9 to 11 , wherein the laser excitation source provides photons in a photon antibunching emission scheme.

13. The quantum random number generator apparatus of any of claims 9 to 12; wherein the laser excitation source is configured to resonantly excite single photon source emission.

14. The quantum random number generator apparatus of any preceding claim, wherein the detector module is configured to: allocate a “1” value to a photon received in the first photon stream; and allocate a “1” value to a photon received in the second photon stream.

15. The quantum random number generator apparatus of any preceding claim, comprising a post-processing module electrically connected to the detector module, the post-processing module configured to: receive a detection signal from the detector module, the detection signal representing the first and second detection signals; and perform, on the received detection signal, one or more of beam splitter asymmetry compensation, entropy distillation, and dark count correction.

16. A quantum random number generation method, comprising: causing a single photon source to undergo resonance fluorescence to generate a stream of single photons; generating, using a beam splitter, a first photon stream and a second photon stream from the stream of single photons; receiving the first photon stream at a first detector to generate a first detection signal from the first photon stream; receiving the second photon stream at a second detector to generate a second detection signal from the second photon stream; receiving the first detection signal and the second detection signal at a detector module; and generating a random number from the first and second detection signals.

17. The quantum random number generation method of claim 16, wherein causing the single photon source to undergo resonance fluorescence to generate a stream of single photons comprises exciting single photon source emission in the single photon source using a continuous-wave laser to cause the single photon source to undergo time-triggered resonance fluorescence; optionally, wherein the continuous wave laser is modulated using an electro-optic modulator.

18. The quantum random number generation method of claim 16 or claim 17, wherein causing the single photon source to undergo resonance fluorescence to generate a stream of single photons comprises exciting single photon source emission in the single photon source at an excitation pulse emission rate of up to 160 MHz, to cause the single photon source to undergo time-triggered resonance fluorescence.

19. The quantum random number generation method of any of claims 16 to 18, wherein causing the single photon source to undergo resonance fluorescence to generate a stream of single photons comprises exciting single photon source emission in the single photon source resonantly to cause the single photon source to undergo time-triggered resonance fluorescence.

20. The quantum random number generator method of any of claims 16 to 19, wherein causing the single photon source to undergo resonance fluorescence to generate a stream of

15 single photons comprises exciting single photon emission from a crystal lattice comprising a defect centre; optionally, wherein the crystal lattice comprises diamond, silicon nitride, silicon carbide, gallium nitride, and boron nitride.

21. The quantum random number generator method of claim 20, wherein exciting single photon emission from the crystal lattice comprising a defect centre comprises exciting single photon emission from a crystal lattice comprising a defect centre wherein the defect centre comprises a trapped vacancy and substitutional atom; optionally, wherein the defect centre is a silicon vacancy centre; a germanium vacancy centre, or a tin vacancy centre.

22. The quantum random number generator method of any of claims 16 to 21 , wherein the method is performed at a temperature between approximately 4K and 300K; preferably, wherein the temperature is between approximately 270K and 300K.

23. The quantum random number generator method of any of claims 16 to 22, wherein causing the single photon source to undergo resonance fluorescence to generate a stream of single photons comprises exciting single photon source emission in a photon antibunching emission scheme.

24. The quantum random number generator method of any of claims 16 to 23, comprising synchronising the first detector with the second detector.

25. A machine-readable medium having program code stored thereon which, when executed by the apparatus of any of claims 1 to 15, causes the machine to perform the operations of any of method 16 to 24.

16