Detailed Office Action
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
Response to Arguments – Amended Claims 1 and 5-13
Applicant’s arguments with respect to amended claims 1 and 5-13 have been considered but are moot because the new ground of rejection does not rely on any reference applied in the prior rejection of record for any teaching or matter specifically challenged in the argument.
As excerpted below, independent claim 1 was amended; dependent claim 2, which depended upon claim 1, was cancelled; dependent claim 3, which depended upon claim 1, and claim 4, which depended upon claim 3, were cancelled.
Excerpts from Amended claim 1 (as filed 26 August 2025)
Excerpts from canceled claim 2, which depended upon claim 1 (as filed 14 April 2023)
Excerpts from canceled claim 3, which depended upon claim 1, and claim 4, which depended upon claim 3 (as filed 14 April 2023)
1. generation of single photons with the predetermined wavelength f_V. ,
wherein at least one of (i) the wavelength of the single photon corresponds to a control variable, (ii) the measured resonator wavelength f_R corresponds to an actual value, or (iii) the predetermined wavelength f_V corresponds to a set point.
wherein in step iii) the controller compares the actual value and the set point and generates the control signal on the basis of the comparison.
2 … wherein steps i) to iv) or step v) form a regulation in the case of or during the generation of single photons with the predetermined wavelength fv,
generates the control signal on the basis of the comparison_
3… wherein the wavelength of the single photon corresponds to a control variable, the measured resonator wavelength fa corresponds to an actual value, and the predetermined wavelength fv corresponds to a set point, and
4… wherein in step iii) the controller compares the actual value and the set point and generates the control signal on the basis of the comparison.
Response to Arguments – Claims 14 and 15
Applicant's arguments filed 26 August 2025 have been fully considered but they are not persuasive. Regarding applicant’s arguments that the prior art combination Vogl, Tobias (Next-generation single-photon sources using two-dimensional hexagonal boron nitride, PhD Thesis, The Australian National University, April 2019; “Vogl-Thesis”) in view of Vogl et al. (Compact Cavity-Enhanced Single-Photon Generation with Hexagonal Boron Nitride, ACS Photonics 2019, 6, 1955−1962, June 2019; “Vogl-NPL”) does not disclose the ‘quoted features’ recited in device claims 14 and 15, the examiner notes that Vogl-Thesis discloses fully integrated and self- contained devices comprising in-situ actuators that can predicably tune resonator cavities to predictably tune single photon wavelengths. Vogl-Thesis, abstract (“The necessary improvement in the photon quality is achieved by coupling an emitter with a microcavity in the Purcell regime. The device is characterized by a strong increase in spectral and single-photon purity … This makes the source among the smallest, fully self-contained, ready-to-operate single-photon sources in the world.”) , page 16 (“The Purcell effect can be exploited to modify the spontaneous emission rate of a single-photon emitter (which is an effective two-level system). Another way to interpret this effect is that the cavity reduces the number of modes the TLS can couple to, thereby enhancing the resonant modes.”), page 52 (“Important for practical applications is that the emitters can be also excited all-electrically in graphene-hBN-TMD heterostructures, without loss of photon quality”), page 55 (“A straightforward path for improving the performance of a spontaneous emission process is to use the Purcell effect by coupling the emitter to an optical resonator[21]. The optical resonator reduces the number of modes the emitter can couple to, thereby enhancing emission into the resonant modes.”), page 126 (“Multilayer hBN flakes have been placed onto the flat mirror via clean polymer transfer (see Methods). The more common direct dry transfer was not used as this usually also transfers residues. The hBN crystals were treated using an oxygen plasma followed by rapid thermal annealing under an Ar atmosphere[20]. Using plasma etching, defects with their ZPL primarily around 560 nm form, well within the stopband of the coating. Finally, a tuneable polymer spacer is deposited onto the concave mirror. A piezoelectric actuator provides the tuning force and compresses the polymer. In contrast to monolithic cavities[44–46], this approach allows for in-situ tuning of the cavity length. The tuning capability is essential, since the exact position of the ZPL cannot yet be controlled and the optical cavity mode has to be artificially matched to the spectrum of the emitter[40]. Due to a suitable Young’s modulus and the ability to deform reversibly, we selected PDMS (polydimethylsiloxane) from a range of polymers (see Supplementary Information S2). Figure 9.1(e) shows that the compression of the PDMS film is linear with the driving voltage at the actuator, with a tuning of 102 nm·V−1. This allows us to easily lock the cavity to any arbitrary wavelength. To prevent influence of the PDMS on the emitter, the PDMS was deposited on the opposing mirror and etched around the array prior to contacting with the other mirror.”), page 129 (“Since the cavity length is tuneable, the single-photon wavelength can also be tuned.”), page 133 (“The cavity also features a linearly tunable PDMS spacer between both mirrors, which allows in-situ tuning of the single-photon line over the full free space ZPL of the quantum emitter. This would allow us to fabricate multiple identical single-photon sources, by locking all to the same emission wavelength, making this approach fully scalable.”), and pages 139-140 (“The complete single-photon source was implemented on a pico-class satellite platform, including excitation laser, driving electronics, and control units.”).
Consequently, applicant’s arguments regarding claims 14 and 15 are not persuasive over the prior art combination Vogl-Thesis in view of Vogl-NPL.
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102 of this title, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries set forth in Graham v. John Deere Co., 383 U.S. 1, 148 USPQ 459 (1966), that are applied for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
This application currently names joint inventors. In considering patentability of the claims the examiner presumes that the subject matter of the various claims was commonly owned as of the effective filing date of the claimed invention(s) absent any evidence to the contrary. Applicant is advised of the obligation under 37 CFR 1.56 to point out the inventor and effective filing dates of each claim that was not commonly owned as of the effective filing date of the later invention in order for the examiner to consider the applicability of 35 U.S.C. 102(b)(2)(C) for any potential 35 U.S.C. 102(a)(2) prior art against the later invention.
Claims 1 and 5-15
Claims 1 and 5-15 are rejected under 35 U.S.C. 103 as being unpatentable over Vogl, Tobias (Next-generation single-photon sources using two-dimensional hexagonal boron nitride, PhD Thesis, The Australian National University, April 2019; available at https://anuquantumoptics.org/site/pdf/theses/2019vogl.pdf; “Vogl-Thesis”) in view of Vogl et al. (Compact Cavity-Enhanced Single-Photon Generation with Hexagonal Boron Nitride, ACS Photonics 2019, 6, 1955−1962, June 2019; DOI: 10.1021/acsphotonics.9b00314; “Vogl-NPL”), and further in view of Carolan et al. (2020/0150511; “Carolan”).
Regarding method claim 1, Vogl-Thesis discloses embodiments of single-photon emitters which, taken in total, encompass structures, devices, and methods for generating specific wavelengths, the structures encompassing resonators and waveguides and the devices and methods encompassing means for predictably tuning the emission processes to achieve application specific-results. See below, for example, Vogl-Thesis: Selected Text, and Vogl-Thesis discloses fully integrated and self- contained devices comprising in-situ actuators that can predicably tune resonator cavities to predictably tune single photon wavelengths. Vogl-Thesis, abstract (“The necessary improvement in the photon quality is achieved by coupling an emitter with a microcavity in the Purcell regime. The device is characterized by a strong increase in spectral and single-photon purity … This makes the source among the smallest, fully self-contained, ready-to-operate single-photon sources in the world.”) , page 16 (“The Purcell effect can be exploited to modify the spontaneous emission rate of a single-photon emitter (which is an effective two-level system). Another way to interpret this effect is that the cavity reduces the number of modes the TLS can couple to, thereby enhancing the resonant modes.”), page 52 (“Important for practical applications is that the emitters can be also excited all-electrically in graphene-hBN-TMD heterostructures, without loss of photon quality”), page 55 (“A straightforward path for improving the performance of a spontaneous emission process is to use the Purcell effect by coupling the emitter to an optical resonator[21]. The optical resonator reduces the number of modes the emitter can couple to, thereby enhancing emission into the resonant modes.”), page 126 (“Multilayer hBN flakes have been placed onto the flat mirror via clean polymer transfer (see Methods). The more common direct dry transfer was not used as this usually also transfers residues. The hBN crystals were treated using an oxygen plasma followed by rapid thermal annealing under an Ar atmosphere[20]. Using plasma etching, defects with their ZPL primarily around 560 nm form, well within the stopband of the coating. Finally, a tuneable polymer spacer is deposited onto the concave mirror. A piezoelectric actuator provides the tuning force and compresses the polymer. In contrast to monolithic cavities[44–46], this approach allows for in-situ tuning of the cavity length. The tuning capability is essential, since the exact position of the ZPL cannot yet be controlled and the optical cavity mode has to be artificially matched to the spectrum of the emitter[40]. Due to a suitable Young’s modulus and the ability to deform reversibly, we selected PDMS (polydimethylsiloxane) from a range of polymers (see Supplementary Information S2). Figure 9.1(e) shows that the compression of the PDMS film is linear with the driving voltage at the actuator, with a tuning of 102 nm·V−1. This allows us to easily lock the cavity to any arbitrary wavelength. To prevent influence of the PDMS on the emitter, the PDMS was deposited on the opposing mirror and etched around the array prior to contacting with the other mirror.”), page 129 (“Since the cavity length is tuneable, the single-photon wavelength can also be tuned.”), page 133 (“The cavity also features a linearly tunable PDMS spacer between both mirrors, which allows in-situ tuning of the single-photon line over the full free space ZPL of the quantum emitter. This would allow us to fabricate multiple identical single-photon sources, by locking all to the same emission wavelength, making this approach fully scalable.”), and pages 139-140 (“The complete single-photon source was implemented on a pico-class satellite platform, including excitation laser, driving electronics, and control units.”).
Vogl-Thesis, Abstract: “[Q]uantum emitters hosted by hBN are attached by van der Waals force to the core of multimode fibers. The system features a free space and fiber-coupled single photon generation mode. The results can be generalized to waveguides and other on-chip photonic quantum information processing devices, thus providing a path toward integration with photonic networks. Next, the fabrication process, based on a microwave plasma etching technique, is substantially improved, achieving a narrow emission linewidth, high single-photon purity, and a significant reduction of the excited state lifetime. The defect formation probability is influenced by the plasma conditions, while the emitter brightness correlates with the annealing temperature.” … “Due to their low size, weight and power requirements, the quantum emitters in hBN are promising candidates as light sources for long-distance satellite-based quantum communication.” … “The next part of this thesis focuses on the feasibility of using these emitters as a light source for quantum key distribution. The necessary improvement in the photon quality is achieved by coupling an emitter with a microcavity in the Purcell regime. The device is characterized by a strong increase in spectral and single-photon purity and can be used for realistic quantum key distribution, thereby outperforming efficient state-of-the art decoy state protocols. Moreover, the complete source is integrated on a 1U CubeSat, a picoclass satellite platform encapsulated within a cube of length 10 cm. This makes the source among the smallest, fully self-contained, ready-to-operate single-photon sources in the world. The emitters are also space-qualified by exposure to ionizing radiation. After irradiation with !-rays, protons and electrons, the quantum emitters show negligible change in photophysics. The space certification study is also extended to other 2D materials, suggesting robust suitability for use of these nanomaterials for space instrumentation.”
Vogl-Thesis, 4.2.3 Integration with photonic structures: “A straightforward path for improving the performance of a spontaneous emission process is to use the Purcell effect by coupling the emitter to an optical resonator.”
Vogl-Thesis, Space-compatible cavity-enhanced single-photon generation with hexagonal boron nitride: “Quantum emitters hosted by hBN can open unique opportunities for single-photon QKD applications, due to the large spread of optical transition lines. It is possible to choose a particular defect with a ZPL coinciding with one of the Fraunhofer lines (e.g. H↵) in the solar spectrum. Narrow filtering around this line allows one to operate the QKD system at daylight, as the background from sunlight at that particular wavelength is suppressed.”
Vogl-Thesis: Selected Text
Page 9 Abstract (“Due to their low size, weight and power requirements, the quantum emitters in hBN are promising candidates as light sources for long-distance satellite-based quantum communication. The next part of this thesis focuses on the feasibility of using these emitters as a light source for quantum key distribution. The necessary improvement in the photon quality is achieved by coupling an emitter with a microcavity in the Purcell regime. The device is characterized by a strong increase in spectral and single-photon purity and can be used for realistic quantum key distribution, thereby outperforming efficient state-of-the-art decoy state protocols. Moreover, the complete source is integrated on a 1U CubeSat, a picoclass satellite platform encapsulated within a cube of length 10 cm. This makes the source among the smallest, fully self-contained, ready-to-operate single-photon sources in the world.”)
Page 16. The Purcell effect can be exploited to modify the spontaneous emission rate of a single-photon emitter (which is an effective two-level system). Another way to interpret this effect is that the cavity reduces the number of modes the TLS can couple to, thereby enhancing the resonant modes.
Page 51. Quantum emitters in 2D materials.
Page 52. Important for practical applications is that the emitters can be also excited all-electrically in graphene-hBN-TMD heterostructures, without loss of photon quality.
Pages 55-56. 4.2.3 Integration with photonic structures
A straightforward path for improving the performance of a spontaneous emission process is to use the Purcell effect by coupling the emitter to an optical resonator[21]. The optical resonator reduces the number of modes the emitter can couple to, thereby enhancing emission into the resonant modes. This even works in the ”bad-emitter” regime, when the emitter linewidth is larger than the cavity linewidth[159]. Furthermore, all cavity QED theory (see Sec. 2.5) still applies, even though the emitter coupled to the cavity is, in this case, a defect in a solid rather than an atom. The dipole transition of the defect acts as a similar effective two-level system.
In addition to the work on cavity-integration of emitters in TMDs, quantum emitters hosted by hBN have been coupled to plasmonic nanocavities as well, achieving a single photon source with a particularly low second-order correlation function[160]. Hexagonal 56 Quantum emitters in 2D materials boron nitride can also be used to fabricate photonic crystal cavities, however, this makes the required spectral matching between optical cavity mode and emitter difficult[161]. The coupling of emitters with a dielectric cavity was recently achieved and is described in Chap. 9[162].
It is also possible to integrate the emitters directly with fibers. This can be achieved by transferring an hBN flake hosting a quantum emitter to a tapered fiber using a tungsten tip driven by a piezo positioner[142]. The overall system collection efficiency was 10%. The same system collection efficiency can be achieved by attaching the hBN flake by van der Waals force onto the core of a multimode fiber[163]. The advantage of the latter is that it does not increase the emitter lifetime. An alternative approach is to directly combine the cavity with the fiber. The fiber tip surface is shaped to be concave using a CO2 laser pulse and subsequently coated to be highly reflecting[164]. This system achieves a high finesse, small mode volume, and features single-photon collection with the fiber. This has been demonstrated for NV and SiV centers in diamond coupled to these fiber microcavities[165, 166].
Page 57. The single-photon sources are ideal for QKD, as they can be fully integrated within a cube with edge length of 10 cm[162], making them interesting for satellite-based quantum key distribution. Their feasibility is confirmed by the temperature stability over a range of 800K[145], long-term stable operation over months[131], as well as resistance to space radiation[66]. The quantum emitters in hBN are particularly useful here due to the spread of optical transition lines. One can choose a defect with a ZPL coinciding with one of the Fraunhofer lines in the solar spectrum. Narrow filtering around this line allows one to operate a QKD system at daylight, as the background from sun light is suppressed[170].
Page 59. Next-generation single-photon sources.
Pages 88-89. 7.5 Correlating optical properties
The optical properties as described in the previous section are by no means representative for all defects, but are typical photophysical properties. The optical properties in terms of spectral distribution, excited state lifetime, power-dependence, photostability, and second order correlation function vary not only from flake to flake but also from defect to defect hosted by the same flake. As reported previously[13], the ZPLs cover the full visible spectrum below the excitation photon energy. In our experiments the quantum emitter ZPLs span a range from 550 to 720 nm, with the lower limit set by a long pass filter used to filter out the excitation laser and the upper limit set by the spectrometer bandwidth. The linewidths vary from as low as 1.31(7) nm (see Figure 7.2(g)) to 11.6(4) nm at room temperature, while the exciton lifetimes span a smaller range from 294(3) ps to 1.32(1) ns1. This is more than 1 order of magnitude faster than any previously reported excited state lifetime in hBN; in fact, all of the defects have shorter lifetimes than the fastest previously reported ones (see also Supporting Information S4). The single-photon purities characterized by g(2) (0) vary from 0.033(47) to 0.480(38) (excluding any emitter with g(2) (0) > 0.5, which are considered ensembles). A single-photon purity with g(2) (0) = 0.033(47) (see Figure 7.2(h)) in hBN is only matched by emitters coupled to plasmonic nanocavity arrays[ 29], with g(2) (0) = 0.02 − 0.04. This defect has a time-bandwidth product of 1389. The slopes of the power saturation vary from 0.290(56) to 0.942(43) for different defects. Across all defects, the optical properties are randomly distributed with the exception of the zero phonon line, which with a 53% chance is between 550 and 570 nm (see Supporting Information S4).
Page 121. Space-compatible cavity-enhanced single-photon generation with hexagonal boron nitride
Pages 121-122. 9.1 Foreword
The previous chapter presented the space qualification of 2D material based devices, which included the single-photon emitters hosted by hexagonal boron nitride. The quantum emitters are projected to survive the harsh radiation environments in space, without any modification in photophysics. For satellite-based single-photon quantum key distribution, however, this certification is only a necessary, but not sufficient condition. Even with the plasma treated hBN, the single-photon source performance is still far from the requirements of quantum information processing, let alone for quantum cryptography or quantum computing.
A straightforward path for enhancing a spontaneous emission process is by coupling the emitter to an optical resonator, known as the Purcell effect. The resonator reduces the photonic density of states, so emission into the resonant modes is enhanced. This cleans the emission spectrum, as any o↵-resonant noise is suppressed. As the emission is predominantly into the resonator modes, the collection efficiency is enhanced. Moreover, as any non-radiative decay path remains unaffected, but radiative decay is enhanced by the Purcell factor, the quantum efficiency is ultimately increased. The increase in radiative decay also shortens the excited state lifetime, which is important for efficient post-selection and the single-photon repetition rate. A cavity linewidth that is narrower than the emitter linewidth can also increase the indistinguishability of consecutively emitted single-photons. This allows one to use even strongly dephasing emitters for photonic quantum computing.
In order to achieve a strong Purcell enhancement, the cavity mode volume must be small, and the cavity quality factor high. A small mode volume can be achieved by utilizing nanofabrication techniques, while for a high quality factor, highly reflecting coatings are required. This chapter presents the results of such a cavity-enhanced emitter. The cavity was fully fabricated at the Australian National Fabrication Facility node at the Australian National University. While the achieved dielectric high-reflection coatings are lagging behind state-of-the-art commercial coatings, having the entire fabrication cycle local allows for fast turn-around times in the device fabrication. The complete single-photon source was implemented on a pico-class satellite platform, including excitation laser, driving electronics, and control units. Thus, this work tests if such a single-photon source can be enhanced such that the performance is sufficient for quantum key distribution, while at the same time being compact enough to fulfill the strict size, weight and power requirements on satellites. This could lead to low-cost satellite-based long-distance quantum networks. The work has been published as an as soon as publishable article in ACS Photonics and is here reprinted (adapted) with permission from https://pubs.acs.org/doi/10.1021/acsphotonics.9b00314. Copyright 2019 American Chemical Society. All graphics have been recreated to match the style of this thesis. A preprint is available at arXiv:1902.03019 (2019).
Page 126 Multilayer hBN flakes have been placed onto the flat mirror via clean polymer transfer (see Methods). The more common direct dry transfer was not used as this usually also transfers residues. The hBN crystals were treated using an oxygen plasma followed by rapid thermal annealing under an Ar atmosphere[20]. Using plasma etching, defects with their ZPL primarily around 560 nm form, well within the stopband of the coating. Finally, a tuneable polymer spacer is deposited onto the concave mirror. A piezoelectric actuator provides the tuning force and compresses the polymer. In contrast to monolithic cavities[44–46], this approach allows for in-situ tuning of the cavity length. The tuning capability is essential, since the exact position of the ZPL cannot yet be controlled and the optical cavity mode has to be artificially matched to the spectrum of the emitter[40]. Due to a suitable Young’s modulus and the ability to deform reversibly, we selected PDMS (polydimethylsiloxane) from a range of polymers (see Supplementary Information S2). Figure 9.1(e) shows that the compression of the PDMS film is linear with the driving voltage at the actuator, with a tuning of 102 nm·V−1. This allows us to easily lock the cavity to any arbitrary wavelength. To prevent influence of the PDMS on the emitter, the PDMS was deposited on the opposing mirror and etched around the array prior to contacting with the other mirror.
Page 129. Since the cavity length is tuneable, the single-photon wavelength can also be tuned.
Page 131. Quantum emitters hosted by hBN can open unique opportunities for single-photon QKD applications, due to the large spread of optical transition lines. It is possible to choose a particular defect with a ZPL coinciding with one of the Fraunhofer lines (e.g. H↵) in the solar spectrum. Narrow filtering around this line allows one to operate the QKD system at daylight, as the background from sunlight at that particular wavelength is suppressed[54].
Page 133 The cavity also features a linearly tunable PDMS spacer between both mirrors, which allows in-situ tuning of the single-photon line over the full free space ZPL of the quantum emitter. This would allow us to fabricate multiple identical single-photon sources, by locking all to the same emission wavelength, making this approach fully scalable.
pages 139-140 The complete single-photon source was implemented on a pico-class satellite platform, including excitation laser, driving electronics, and control units. Thus, this work tests if such a single-photon source can be enhanced Space-compatible cavity-enhanced single-photon generation with hexagonal boron nitride such that the performance is sufficient for quantum key distribution, while at the same time being compact enough to fulfill the strict size, weight and power requirements on satellites.
Pages 150-153 9.6 Conclusion. We have demonstrated coupling of a quantum emitter hosted by multilayer hBN to a confocal microcavity. The hemispherical geometries have been fabricated using FIB milling with sub-nm precision. The cavity mode volume is of the order of 03. The cavity improves the spectral purity of the emitter substantially, with the FWHM decreasing from 5.76 to 0.224 nm. Moreover, the cavity suppresses o↵-resonant noise, which allows us to improve its single-photon purity. The excited state lifetime of the emitter is also shortened by the Purcell effect by a factor of 2.3. The emission of the cavity is linearly polarized and stable over long timeframes, with no signs of photobleaching or blinking. The cavity also features a linearly tunable PDMS spacer between both mirrors, which allows in-situ tuning of the single-photon line over the full free space ZPL of the quantum emitter. This would allow us to fabricate multiple identical single-photon sources, by locking all to the same emission wavelength, making this approach fully scalable. Furthermore, the complete SPS is portable and fully self-contained within 10 ⇥ 10 ⇥ 10 cm3, the size of a 1U CubeSat. This makes the single-photon source a promising candidate for low cost satellite-based long-distance QKD, especially as the quantum emitters in hBN are space certified. Despite the source’s performance being not yet sufficient for one-way quantum computing, using the single-photon source for QKD even now enhances the quantum key generation rate on useful distances. The microcavity platform can also be easily adapted to other quantum emitters in 2D materials and offers a promising path towards scalable quantum information processing.”) and Cavity alignment (“The emitter on the mirror has been located and characterized in free-space. The hBN flake capable of hosting a defect (determined by flake thickness) was centered onto the mirror, making it easy to locate on the mirror. Nearby crystal flakes serve as markers for localizing the flake with the pre-characterized defect. For aligning the crystal long working distance objectives in a custom-built microscope have been used, illuminated with a near infrared LED where all coatings are transparent. Each component, held and aligned with vacuum tweezers on a motorized 6-axis nanopositioning stage, is glued one after another. arXiv:1902.03019 (2019) 135 The adhesive used was UHU Plus Endfest 300, a two component epoxy glue and was cured for 24 hours at room temperature. Where required a second layer of glue was added and cured for another 24 hours. Diagnostics were used to provide feedback for a good alignment, e.g. single-photon detection rate when aligning the cavity, combined with the spectrometer to check the cavity mode profile.
Pages 161 – 162. Conclusions
This thesis presented advances in developing optically active defects hosted by two dimensional hexagonal boron nitride for quantum information processing. These defects act as an idealized two-level system that, after excitation with a laser, emit a single-photon as they relax to their initial ground state. A single-photon source is a crucial key building block for optical quantum technologies, including quantum cryptography and quantum computing.
Hexagonal boron nitride as a host material for these defects has the decisive advantage of a wide band gap, which isolates the deep defect states from the energy band edges, as well as prevents non-radiative decay of the excited state. The former allows for operation at room temperature, while the latter leads to an ultrahigh single-photon luminosity and quantum yield. In addition, the 2D lattice of hBN allows for an intrinsically ideal extraction efficiency of generated single-photons.
Among the milestones achieved in this thesis is a quantum emitter attached by van der Waals force to the core of a multimode fiber. This system achieved an overall collection efficiency of 10% and was able to generate free space and fiber-coupled single-photons solely depending on the excitation direction. The fabrication process was subsequently improved through plasma etching, achieving emission linewidths 1nm, g(2)(0) = 0.03 and excited state lifetimes as short as 294 ps. Furthermore, the emitters were stable over the entire duration of the experiments, with no significant changes in photophysics observed. It was also possible to transfer these emitters to arbitrary new substrates, allowing for the fabrication of on-chip single-photon sources.
A highlight of this thesis is the space qualification of 2D materials and devices based on them, including the quantum emitters in hBN, as well as atomically thin field-effect transistors. This study proved that quantum emitters in hBN can be used in orbit on satellites for quantum key distribution schemes. Moreover, the transistors survived the harsh conditions of space without degradation in performance, suggesting robust suitability for space instrumentation and satellite electronics. This was also extended to a variety of monolayered 2D materials as building blocks for future electronics and optoelectronics. Interestingly, under excess !-radiation, monolayer WS2 showed decreased defect densities, identified by an increase in photoluminescence, carrier lifetime and a change in doping ratio proportional to the photon flux. The underlying mechanism is traced back to radiation-induced defect healing, wherein dissociated oxygen passivates sulfur vacancies. An application of this remarkable effect could be a radiation detector.
Another highlight is the implementation of the single-photon source on a satellite platform. Due to its low size, weight and power requirements, the source is predisposed for the use on satellites or other mobile applications where strict limitations apply. The complete single-photon source was implemented on a 1U CubeSat, a picoclass satellite with a volume of 10 ⇥ 10 ⇥ 10 cm3 and a maximal payload weight of 1.33 kg. The source was fully self-contained and ready-to-operate with the excitation laser, all driving electronics and control units, including a single board computer onboard the CubeSat. Therefore, this makes the source among the smallest single-photon sources in the world.
Moreover, the single-photon emission process was enhanced by an optical resonator in the Purcell regime. This increased the spontaneous emission rate, spectral and single-photon purity as well as the quantum yield and collection efficiency. The performance so far allowed one to evaluate the source for quantum key distribution protocols, thereby outperforming the most efficient decoy protocols which are conventionally used in quantum cryptography on short and medium distances. Therefore, this work provides a path toward low-cost satellite-based long-distance quantum communication networks, the backbone of a future quantum internet. Finally, efforts have been made to locate the emitters with atomic precision, with the result that the positions, at which the defects form, correlate with the fabrication method. This in turn allows one to specifically engineer the emitters and optical properties influenced by the emitter location.
Whether the emitters are indeed useful for quantum key distribution applications has yet to be demonstrated. This is left to a future experiment. The figure of merit which the experiment has to be benchmarked against is the secret key rate, and only if the single photon source yields a higher secret key rate, it will be interesting for QKD. The simulations of the QKD experiments so far used some approximations and neglected second-order effects, but it is still expected that the advantage over decoy state protocols at short and medium distances will prevail. Further improvements can also enhance the single-photon quality even more, thus extending the usable distance the single-photon source can be used for in QKD applications. It would also be advantageous to have an electrical excitation scheme, which would reduce the complexity of the single-photon source substantially. Due to the insulating nature of hBN, however, this is not straightforward to achieve. Another application for a satellite-based single-photon source is a fundamental test of quantum mechanics. Such experiment would search for physics beyond the standard model that could be probed with quantum optics. Examples for such theories are higher-order interference and hyper-complex quantum mechanics, expanded with a coupling strength to a gravitational field. The required single-photon interferometer has already been developed during this PhD, but the experiments are still ongoing and will continue in the future.
To summarize the work in a final remark, this thesis lays a strong foundation for future applications of single-photon sources based on hexagonal boron nitride and two dimensional materials for space instrumentation. This predominantly applies to quantum communication, with the developed single-photon source as one of the key building blocks in a global quantum network. Further improvements of the device performance will expand the range of applications, some of which still have to be discovered and explored.
Further regarding claim 1, while Vogl-Thesis discusses a complete device; Vogl-Thesis, page 123; Vogl-Thesis does not a single specific embodiment that explicitly and inherently comprises a method for generating single photons with a predetermined wavelength f_V comprising: i) generating a single photon, wherein the single photon has a resonator wavelength f_R and a resonator bandwidth f_BR; ii) measuring the resonator wavelength f_R, wherein the single photon is guided from a resonator to a wavelength standard via a beam guide; iii) comparing the resonator wavelength f_R with the predetermined wavelength f_V and generating a control signal on the basis of the comparison; iv) adjusting the resonator using the control signal in order to change the resonator wavelength f_R toward or to the predetermined wavelength f_V; and v) repeating steps i to iv) until the resonator wavelength f_R corresponds to the predetermined wavelength f_V and then coupling out a single photon with a predetermined wavelength f_V into an output.
However, Vogl-NPL discloses in figures 1-3, and related text, for example, Vogl-NPL-Selected Text, incorporating hBN-hosted quantum emitters into a, “complete device, including all optics, driving electronics, and control units, is compact and integrated in a small volume of 10 × 10 × 10 cm3, allowing for portable usage in mobile applications.” Vogl-NPL, abstract.
Vogl-NPL: Figure 1
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Vogl-NPL: Figure 2
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Vogl-NPL: Figure 3
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Vogl-NPL: Selected Text
ABSTRACT: Sources of pure and indistinguishable single photons are critical for near-future optical quantum technologies. Recently, color centers hosted by two-dimensional hexagonal boron nitride (hBN) have emerged as a promising platform for high luminosity room temperature single-photon sources. Despite the brightness of the emitters, the spectrum is rather broad and the single-photon purity is not sufficient for practical quantum information processing. Here, we report integration of such a quantum emitter hosted by hBN into a tunable optical microcavity. A small mode volume of the order of λ3 allows us to Purcell enhance the fluorescence, with the observed excited state lifetime shortening. The cavity significantly narrows the spectrum and improves the single-photon purity by suppression of off-resonant noise. The complete device, including all optics, driving electronics, and control units, is compact and integrated in a small volume of 10 × 10 × 10 cm3, allowing for portable usage in mobile applications.
Page 1959. Performance of the Single-Photon Source (“Since the cavity length is tunable, the single-photon wavelength can also be tuned. Effectively, the tuning range is the line width of the free-space emission. The cavity is only sampling the free-space emission spectrum, however, so the actual single-photon count rate is the spectral overlap integral of optical cavity mode and emitter. This results in the emission rate decreasing with increasing cavity detuning.”)
Page 1960. CONCLUSION. We have demonstrated coupling of a quantum emitter hosted by multilayer hBN to a confocal microcavity. The hemispherical geometries have been fabricated using FIB milling with sub-nm precision. The cavity mode volume is of the order of λ3. The cavity improves the spectral purity of the emitter substantially, with the fwhm decreasing from 5.76 to 0.224 nm. Moreover, the cavity suppresses off-resonant noise, which allows us to improve its single-photon purity. The excited state lifetime of the emitter is also shortened by the Purcell effect by a factor of 2.3. The emission of the cavity is linearly polarized and stable over long timeframes, with no signs of photobleaching or blinking. The cavity also features a linearly tunable PDMS spacer between both mirrors, which allows in situ tuning of the single-photon line over the full free-space ZPL of the quantum emitter. This would allow us to fabricate multiple identical single-photon sources, by locking all to the same emission wavelength, making this approach fully scalable. Furthermore, the complete SPS is portable and fully selfcontained within 10 × 10 × 10 cm3. The microcavity platform can also be easily adapted to other quantum emitters in 2D materials and offers a promising path toward scalable quantum information processing.
Page 1960. Methods. We utilize linear variable filters (Delta Optical Thin Film 3G LVLWP and 3G LVSWP) to tune center and bandwidth of the band-pass filtering system.
Consequently, it would have been obvious to one of ordinary skill in the art to modify the devices and methods disclosed by Vogl-Thesis, in accordance with the “complete device” and methods disclosed by Vogl-NPL, to disclose a method for generating single photons with a predetermined wavelength f_V comprising: i) generating a single photon, wherein the single photon has a resonator wavelength f_R and a resonator bandwidth f_BR; ii) measuring the resonator wavelength f_R, wherein the single photon is guided from a resonator to a wavelength standard via a beam guide; iii) comparing the resonator wavelength f_R with the predetermined wavelength f_V and generating a control signal on the basis of the comparison; iv) adjusting the resonator using the control signal in order to change the resonator wavelength f_R toward or to the predetermined wavelength f_V; and v) repeating steps i to iv) until the resonator wavelength f_R corresponds to the predetermined wavelength f_V and then coupling out a single photon with a predetermined wavelength f_V into an output; See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text; because the resulting structures and methods would facilitate designing, fabricating and deploying, “[A]complete device, including all optics, driving electronics, and control units, [that] is compact and integrated in a small volume of 10 × 10 × 10 cm3, allowing for portable usage in mobile applications.” Vogl-NPL, abstract.
Further regarding claim 1, Carolan discloses in figures 1-6, and related text, “[A]n in situ frequency-locking technique monitors and corrects frequency variations in single-photon sources based on resonators. By using the classical laser fields used for photon generation as probes to diagnose variations in the resonator frequency, the system applies feedback control to correct photon frequency errors in parallel to the optical quantum computation without disturbing the physical qubit. Our technique can be implemented on a silicon photonic device and with sub 1 pm frequency stabilization in the presence of applied environmental noise, corresponding to a fractional frequency drift of <1% of a photon linewidth. These methods can be used for feedback-controlled quantum state engineering. By distributing a single local oscillator across a one or more chips, our approach enables frequency locking of many single photon sources for large-scale photonic quantum technologies.” Carolan, abstract.
Consequently, it would have been obvious to one of ordinary skill in the art to modify the devices and methods disclosed by Vogl-Thesis, in accordance with the “complete device” and methods disclosed by Vogl-NPL, to disclose a method for generating single photons with a predetermined wavelength fv comprising: i) generating a single photon, wherein the single photon has a resonator wavelength fR and a resonator bandwidth fBR; ii) measuring the resonator wavelength fR, wherein the single photon is guided from a resonator to a wavelength standard via a beam guide; iii) comparing the resonator wavelength fR with the predetermined wavelength fv and generating a control signal on the basis of the comparison in a controller; iv) adjusting the resonator using the control signal in order to change the resonator wavelength fR toward or to the predetermined wavelength fv; and v) repeating steps i to iv) until the resonator wavelength fR corresponds to the predetermined wavelength fv and then coupling out a single photon with a predetermined wavelength fv into an output, wherein steps i) to iv) or step v) form a regulation in the case of or during the generation of single photons with the predetermined wavelength fv, wherein the wavelength of the single photon corresponds to a control variable, the measured resonator wavelength fR corresponds to an actual value, and the predetermined wavelength fv corresponds to a set point, and wherein in step iii) the controller compares the actual value and the set point and generates the control signal on the basis of the comparison; See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text.; Carolan, figures 1-6, and related text; because the resulting structures and methods would facilitate designing, fabricating and deploying, “[A]complete device, including all optics, driving electronics, and control units, [that] is compact and integrated in a small volume of 10 × 10 × 10 cm3, allowing for portable usage in mobile applications;” Vogl-NPL, abstract; for frequency locking multiple single photon sources in large-scale photonic quantum technologies.
Regarding dependent method claims 5-13, it would have been obvious to one of ordinary skill in the art to modify the devices and methods disclosed by Vogl-Thesis, in accordance with the “complete device” and methods disclosed by Vogl-NPL, and further in view of Carolan, as applied in the rejection of claim 1, to disclose:
5. The method for generating single photons with a predetermined wavelength f_V according to claim 1, wherein the method comprises: a) measuring the resonator wavelength f_R in the wavelength standard as measuring device, and c) adjusting the resonator using the control signal as actuating means. See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text; Carolan, figures 1-6, and related text.
6. The method for generating single photons with a predetermined wavelength f_V according to claim 1, wherein steps i) to iv) are repeated until the resonator wavelength f_R of the single photon generated in step i) lies in a range of ±0.2 nm, around the predetermined wavelength f_V. See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text; Carolan, figures 1-6, and related text.
7. The method for generating single photons with a predetermined wavelength f_V according to claim 1, wherein the predetermined wavelength f_V is a Fraunhofer line. See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text; Carolan, figures 1-6, and related text.
8. The method for generating single photons with a predetermined wavelength f_V according to claim 1, wherein the single photon is generated in step i) by spontaneous emission or spontaneous parametric conversion. See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text; Carolan, figures 1-6, and related text.
9. The method for generating single photons with a predetermined wavelength f_V according to claim 1, wherein in step i) source is excited by the resonator to emit the single photon with a resonator wavelength f_R and a resonator bandwidth f_BR, or the source generates a single photon with a source wavelength f_Q and a source bandwidth f_BQ and the resonator filters therefrom a single photon which has the resonator wavelength f_R and the resonator bandwidth f_BR, wherein the predetermined wavelength f_V and the resonator wavelength f_R are contained in the range of the source bandwidth f_BQ. See above, Vogl-Thesis: Selected Text; See above, Vogl-NPL, figures 1-3, and related text, for example, see above, Vogl-NPL: Selected Text; Carolan, figures 1-6, and related text.
10. The method for generating single photons with a predetermined wavelength f_V according to claim 1, wherein in step iv) the resonator is regulated or is formed so that the resonator can be regulated at least one of chemically, thermally, electrically, mechanically or optically. See above, Vogl-Thesis: Selected Text; See above, Vogl-N