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Physical unclonable functions (PUFs) have emerged as a promising encryption technology, utilizing intrinsic physical identifiers that offer enhanced security and tamper resistance. Multi‐level PUFs boost system complexity, thereby improving system reliability and fault tolerance. However, crosstalk‐free multi‐level PUFs remain a persistent challenge. In this study, a hierarchical PUF system that harnesses the spontaneous phase separation of silk fibroin /PVA blend and the random distribution of silicon‐vacancy diamonds within the blend is presented. The thermodynamic instability of phase separation and inherent unpredictability of diamond dispersion gives rise to intricate random patterns at two distinct scales, enabling time‐efficient hierarchical authentication for cryptographic keys. These patterns are complementary yet independent, inherently resistant to replication and damage thus affording robust security and reliability to the proposed system. Furthermore, customized authentication algorithms are constructed: visual PUFs authentication utilizes neural network combined structural similarity index measure, while spectral PUFs authentication employs Hamming distance and cross‐correlation bit operation. This hierarchical PUF system attains a high recognition rate without interscale crosstalk. Additionally, the coding capacity is exponentially enhanced using M‐ary encoding to reinforce multi‐level encryption. Hierarchical PUFs hold significant potential for immediate application, offering unprecedented data protection and cryptographic key authentication capabilities. [ABSTRACT FROM AUTHOR]

Diamond color centers have proven to be versatile quantum emitters and exquisite sensors of stress, temperature, electric and magnetic fields, and biochemical processes. Among color centers, the silicon-vacancy (SiV-) defect exhibits high brightness, minimal phonon coupling, narrow optical linewidths, and high degrees of photon indistinguishability. Yet the creation of reliable and scalable SiV--based color centers has been hampered by heterogeneous emission, theorized to originate from surface imperfections, crystal lattice strain, defect symmetry, or other lattice impurities. Here, we advance high-resolution cryo-electron microscopy combined with cathodoluminescence spectroscopy and 4D scanning transmission electron microscopy (STEM) to elucidate the structural sources of heterogeneity in SiV- emission from nanodiamond with sub-nanometer-scale resolution. Our diamond nanoparticles are grown directly on TEM membranes from molecular-level seedings, representing the natural formation conditions of color centers in diamond. We show that individual subcrystallites within a single nanodiamond exhibit distinct zero-phonon line (ZPL) energies and differences in brightness that can vary by 0.1 meV in energy and over 70% in brightness. These changes are correlated with the atomic-scale lattice structure. We find that ZPL blueshifts result from tensile strain, while ZPL red shifts are due to compressive strain. We also find that distinct crystallites host distinct densities of SiV- emitters and that grain boundaries impact SiV- emission significantly. Finally, we interrogate nanodiamonds as small as 40 nm in diameter and show that these diamonds exhibit no spatial change to their ZPL energy. Our work provides a foundation for atomic-scale structure-emission correlation, e.g., of single atomic defects in a range of quantum and two-dimensional materials. [ABSTRACT FROM AUTHOR]

In this work, we successfully integrated fluorescent nanodiamonds (FNDs) and lanthanide ion-doped upconversion nanoparticles (UCNPs) in a nanocomposite structure for simultaneous optical temperature sensing. The effective integration of FND and UCNP shells was confirmed by employing high-resolution TEM imaging, X-ray diffraction, and dual-excitation optical spectroscopy. Furthermore, the synthesized ND@UCNP nanocomposites were tested by making simultaneous optical temperature measurements, and the detected temperatures showed excellent agreement within their sensitivity limit. The simultaneous measurement of temperature using two different modalities having different sensing physics but with the same composite nanoparticles inside is expected to greatly improve the confidence of nanoscale temperature measurements. This should resolve some of the controversy surrounding nanoscale temperature measurements in biological applications. [ABSTRACT FROM AUTHOR]

Abstract Physical unclonable functions (PUFs) have emerged as a promising encryption technology, utilizing intrinsic physical identifiers that offer enhanced security and tamper resistance. Multi‐level PUFs boost system complexity, thereby improving system reliability and fault tolerance. However, crosstalk‐free multi‐level PUFs remain a persistent challenge. In this study, a hierarchical PUF system that harnesses the spontaneous phase separation of silk fibroin /PVA blend and the random distribution of silicon‐vacancy diamonds within the blend is presented. The thermodynamic instability of phase separation and inherent unpredictability of diamond dispersion gives rise to intricate random patterns at two distinct scales, enabling time‐efficient hierarchical authentication for cryptographic keys. These patterns are complementary yet independent, inherently resistant to replication and damage thus affording robust security and reliability to the proposed system. Furthermore, customized authentication algorithms are constructed: visual PUFs authentication utilizes neural network combined structural similarity index measure, while spectral PUFs authentication employs Hamming distance and cross‐correlation bit operation. This hierarchical PUF system attains a high recognition rate without interscale crosstalk. Additionally, the coding capacity is exponentially enhanced using M‐ary encoding to reinforce multi‐level encryption. Hierarchical PUFs hold significant potential for immediate application, offering unprecedented data protection and cryptographic key authentication capabilities.

Boron-doped nanodiamonds (BNDs) have recently shown a promising potential in hyperthermia and thermoablation therapy, especially in heating tumor cells. To remotely monitor eigen temperature during such operations, diamond color centers have shown a sensitive optical temperature sensing. Nitrogen-vacancy (NV) color center in diamonds have shown the best sensitivity in nanothermometry; however, spin manipulation of the NV center with green laser and microwave-frequency excitations is still a huge challenge for biological applications. Silicon-vacancy (SiV) color center in nano/bulk diamonds has shown a great potential to be a good replacement of the NV center in diamond as it can be excited and detected within the biological transparency window and its thermometry operations depends only on its zero-phonon line (ZPL) shift as a function of temperature changes. In this work, BNDs were carefully etched on smooth diamond nanocrystals' sharp edges and implanted with silicon for optical temperature sensing. Optical temperature sensing using SiV color centers in BNDs was performed over a small range of temperature within the biological temperature window (296–308 K) with an excellent sensitivity of 0.2 K in 10 s integration time. These results indicate that there are likely to be better application of more biocompatible BNDs in hyperthermia and thermoablation therapy using a biocompatible diamond color center. [ABSTRACT FROM AUTHOR]

In this work, we successfully integrated fluorescent nanodiamonds (FNDs) and lanthanide ion-doped upconversion nanoparticles (UCNPs) in a nanocomposite structure for simultaneous optical temperature sensing. The effective integration of FND and UCNP shells was confirmed by employing high-resolution TEM imaging, X-ray diffraction, and dual-excitation optical spectroscopy. Furthermore, the synthesized ND@UCNP nanocomposites were tested by making simultaneous optical temperature measurements, and the detected temperatures showed excellent agreement within their sensitivity limit. The simultaneous measurement of temperature using two different modalities having different sensing physics but with the same composite nanoparticles inside is expected to greatly improve the confidence of nanoscale temperature measurements. This should resolve some of the controversy surrounding nanoscale temperature measurements in biological applications.

The high quality of crystal growth and advanced fabrication technology of silicon carbide (SiC) in power electronics enables the control of optically active defects in SiC, such as silicon vacancies (VSi). In this paper, VSi are generated in hexagonal SiC (4H) samples through ion implantation of nitrogen or (and) aluminum, respectively the n- and p-type dopants for SiC. The presence of silicon vacancies within the samples is studied using cathodoluminescence at 80K. For 4H-SiC samples, the ZPL (zero phonon line) of the V1′ center of VSi is more intense than the one for the V1 center before annealing. The opposite is true after 900 °C annealing. ZPLs of the divacancy defect (VCVSi) are also visible after annealing. [ABSTRACT FROM AUTHOR]

Point defects in silicon carbide (SiC) formed after ion implantation can serve as color centers for quantum sensing, or as donors or acceptors to provide carriers to influence electrical performance. Confocal spectroscopic characterization allows the determination of point defect-related optical and electrical properties without sample preparation or destruction. However, phenomena such as refraction and aberration can complicate the interpretation of the results of three-dimensional spectroscopy. Here, we used H+, N+ and He+ implantation to fabricate silicon vacancy (V Si) color centers in SiC with zero phonon lines (ZPLs) at around 900 nm and used confocal spectroscopy to characterize bulk and thin layer of V Si contained materials. 270 keV H+ is more advantageous than 150 keV N+ in preparing V Si due to the preservation of better lattice integrity. For thin-layer V Si samples, the photoluminescence intensity maxima of V Si were distributed at 2–6.5 μm above the surface. To explain such confusing phenomenon in depth profiles focusing on and above the surface, the effective excitation volume and chromatic aberration are discussed and proposed for explanation of the results. Furthermore, the ion-implanted layer exhibits a non-negligible effect on the underlying signal during confocal spectral depth profiling, which is attributed to the refraction-related focus degradation. [ABSTRACT FROM AUTHOR]

The negatively charged silicon vacancy VSi−$\left({\mathrm{V}}_{\mathrm{S}\mathrm{i}}^{-}\right)$ in silicon carbide is a well-studied point defect for quantum applications. At the same time, a closer inspection of ensemble photoluminescence and electron paramagnetic resonance measurements reveals an abundance of related but so far unidentified signals. In this study, we search for defects in 4H-SiC that explain the above magneto-optical signals in a defect database generated by automatic defect analysis and qualification (ADAQ) workflows. This search reveals only one class of atomic structures that exhibit silicon-vacancy-like properties in the data: a carbon antisite (CSi) within sub-nanometer distances from the silicon vacancy only slightly alters the latter without affecting the charge or spin state. Such a perturbation is energetically bound. We consider the formation of VSi−+CSi${\mathrm{V}}_{\mathrm{S}\mathrm{i}}^{-}+{\mathrm{C}}_{\mathrm{S}\mathrm{i}}$ up to 2 nm distance and report their zero phonon lines and zero field splitting values. In addition, we perform high-resolution photoluminescence experiments in the silicon vacancy region and find an abundance of lines. Comparing our computational and experimental results, several configurations show great agreement. Our work demonstrates the effectiveness of a database with high-throughput results in the search for defects in quantum applications.

Boron-doped nanodiamonds (BNDs) have recently shown a promising potential in hyperthermia and thermoablation therapy, especially in heating tumor cells. To remotely monitor eigen temperature during such operations, diamond color centers have shown a sensitive optical temperature sensing. Nitrogen-vacancy (NV) color center in diamonds have shown the best sensitivity in nanothermometry; however, spin manipulation of the NV center with green laser and microwave-frequency excitations is still a huge challenge for biological applications. Silicon-vacancy (SiV) color center in nano/bulk diamonds has shown a great potential to be a good replacement of the NV center in diamond as it can be excited and detected within the biological transparency window and its thermometry operations depends only on its zero-phonon line (ZPL) shift as a function of temperature changes. In this work, BNDs were carefully etched on smooth diamond nanocrystals’ sharp edges and implanted with silicon for optical temperature sensing. Optical temperature sensing using SiV color centers in BNDs was performed over a small range of temperature within the biological temperature window (296–308 K) with an excellent sensitivity of 0.2 K in 10 s integration time. These results indicate that there are likely to be better application of more biocompatible BNDs in hyperthermia and thermoablation therapy using a biocompatible diamond color center.

Silicon vacancy (V Si ) centers in 4H-silicon carbide have emerged as a strong candidate for quantum networking applications due to their robust electronic and optical properties, including a long spin coherence lifetime and bright, stable emission. Here, we report the integration of V Si centers with a plasmonic nanocavity to Purcell enhance the emission, which is critical for scalable quantum networking. Employing a simple fabrication process, we demonstrate plasmonic cavities that support a nanoscale mode volume and exhibit an increase in the spontaneous emission rate with a measured Purcell factor of up to 48. In addition to investigating the optical resonance modes, we demonstrate an improvement in the optical stability of the spin-preserving resonant optical transitions relative to the radiation-limited value. The results highlight the potential of nanophotonic structures for advancing quantum networking technologies and emphasize the importance of optimizing emitter-cavity interactions for efficient quantum photonic applications.

The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.

Masers as telecommunication amplifiers have been known for decades, yet their application is strongly limited due to extreme operating conditions requiring vacuum techniques and cryogenic temperatures. Recently, a new generation of masers has been invented based on optically pumped spin states in pentacene and diamond. In this study, we pave the way for masers based on spin S = 3/2 silicon vacancy (VSi) defects in silicon carbide (SiC) to overcome the microwave generation threshold and discuss the advantages of this highly developed spin hosting material. To achieve population inversion, we optically pump the VSi into their mS = ±1/2 spin sub-states and additionally tune the Zeeman energy splitting by applying an external magnetic field. In this way, the prerequisites for stimulated emission by means of resonant microwaves in the 10 GHz range are fulfilled. On the way to realising a maser, we were able to systematically solve a series of subtasks that improved the underlying relevant physical parameters of the SiC samples. Among others, we investigated the pump efficiency as a function of the optical excitation wavelength and the angle between the magnetic field and the defect symmetry axis in order to boost the population inversion factor, a key figure of merit for the targeted microwave oscillator. Furthermore, we developed a high-Q sapphire microwave resonator (Q = 104-105) with which we find superradiant stimulated microwave emission. In summary, SiC with optimized spin defect density and thus spin relaxation rates is well on its way of becoming a suitable maser gain material with wide-ranging applications. [ABSTRACT FROM AUTHOR]

Silicon vacancies in silicon carbide (SiC) have been proposed as interesting candidates for quantum technology applications such as quantum sensing and quantum repeaters. SiC exists in many polytypes with different plane stacking sequences, and in each polytype, the vacancies can occupy a variety of different lattice sites. In this work, we focus on the three important charged silicon vacancies in the 6 H -SiC polytype. We record the photoluminescence and continuous-wave optically detected magnetic resonance (ODMR) spectra at different radio-frequency power levels and different temperatures. We individually select the zero-phonon lines of the different silicon vacancies at low temperatures and record the corresponding ODMR spectra. ODMR allows us to correlate optical and magnetic resonance spectra and thereby separate signals from V _1 and V _3 . The results also explain the observed sign change of the ODMR signal as a function of temperature.

Phonons are envisioned as coherent intermediaries between different types of quantum systems. Engineered nanoscale devices, such as optomechanical crystals (OMCs), provide a platform to utilize phonons as quantum information carriers. Here we demonstrate OMCs in diamond designed for strong for interactions between phonons and a silicon vacancy (SiV) spin. Using optical measurements at millikelvin temperatures, we measure a line width of 13 kHz ( Q -factor of ∼4.4 × 10 5 ) for a 6 GHz acoustic mode, a record for diamond in the GHz frequency range and within an order of magnitude of state-of-the-art line widths for OMCs in silicon. We investigate SiV optical and spin properties in these devices and outline a path toward a coherent spin-phonon interface.

Silicon vacancy centers (SiVs) in diamond have emerged as a promising platform for quantum sciences due to their excellent photostability, minimal spectral diffusion, and substantial zero-phonon line emission. However, enhancing their slow nanosecond excited-state lifetime by coupling to optical cavities remains an outstanding challenge, as current demonstrations are limited to ∼10-fold. Here, we couple negatively charged SiVs to sub-diffraction-limited plasmonic cavities and achieve an instrument-limited ≤8 ps lifetime, corresponding to a 135-fold spontaneous emission rate enhancement and a 19-fold photoluminescence enhancement. Nanoparticles are printed on ultrathin diamond membranes on gold films which create arrays of plasmonic nanogap cavities with ultrasmall volumes. SiVs implanted at 5 and 10 nm depths are examined to elucidate surface effects on their lifetime and brightness. The interplay between cavity, implantation depth, and ultrathin diamond membranes provides insights into generating ultrafast, bright SiV emission for next-generation diamond devices.

Optically detected magnetic resonance with temperature sweep is developed using the temperature dependence of the spin Hamiltonian parameters of paramagnetic color centers in silicon carbide. The detection is based on natural optical alignment of spin level populations over a wide temperature range including room temperature and on the change of these populations during level anti-crossing or cross-relaxation processes. [ABSTRACT FROM AUTHOR]

Different deposition parameters, for the growth of (111)-oriented single crystalline diamond samples were varied, such as temperature, methane concentration, methane/oxygen ratio and chamber pressure. It was shown that good quality material can be deposited at low methane concentrations with oxygen addition at high temperatures. Therefore, a growth temperature of 850 °C is used along with a pressure of 200 mbar, a CH 4 /O 2 ratio of 3 and a methane concentration of 0.3% in order to prevent the incorporation of silicon in the single crystal diamond. Diamond layers with a thickness of 100 nm and 300 μm show RMS roughness values of around 0.26 nm and 200 nm, respectively. [ABSTRACT FROM AUTHOR]

All-optical nanothermometry has become a powerful, remote tool for measuring nanoscale temperatures in applications ranging from medicine to nano-optics and solid-state nanodevices. The key features of any candidate nanothermometer are brightness, sensitivity, and (signal, spatial, and temporal) resolution. Here, we demonstrate a real-time, diamond-based nanothermometry technique with excellent sensitivity (1.8% K -1 ) and record-high resolution (5.8 × 10 4 K Hz -1/2 W cm -2 ) based on codoped nanodiamonds. The distinct performance of our approach stems from two factors: (i) temperature sensors─nanodiamonds cohosting two group IV color centers─engineered to emit spectrally separated Stokes and anti-Stokes fluorescence signals under excitation by a single laser source and (ii) a parallel detection scheme based on filtering optics and high-sensitivity photon counters for fast readout. We demonstrate the performance of our method by monitoring temporal changes in the local temperature of a microcircuit and a MoTe 2 field-effect transistor. Our work advances a powerful, alternative strategy for time-resolved temperature monitoring and mapping of micro-/nanoscale devices such as microfluidic channels, nanophotonic circuits, and nanoelectronic devices, as well as complex biological environments such as tissues and cells.

The non-bridging oxygen hole center (NBOHC) can decrease the transmission efficiency of the amorphous silica (α -Si O 2) material. In radiation environments, the NBOHC can be produced by both the electronic (S e) and the nuclear (S n) energy loss processes of the radiations. The S e -related formation channels of NBOHC have been well characterized. The S n can produce isolated silicon vacancies within α -Si O 2 by knocking out silicon atoms. With first principle calculations, this work investigates the characteristics of the silicon-vacancy defective α -Si O 2 cells, including atomic configuration, electronic density of state and optical absorption coefficient. The stable states of the silicon vacancy defects suggest a direct and an indirect S n -related formation channels for NBOHC. The silicon vacancy has two stable configurations, i.e., the case I contains two NBOHC along with a peroxy linkage (POL), and the case II has two POL. Thereafter, the S e can promote the transition from POL to NBOHC. [ABSTRACT FROM AUTHOR]

Colour centres in nanodiamonds are an important resource for applications in quantum sensing, biological imaging, and quantum optics. Here we report unprecedented narrow optical transitions for individual colour centres in nanodiamonds smaller than 200 nm. This demonstration has been achieved using the negatively charged silicon vacancy centre, which has recently received considerable attention due to its superb optical properties in bulk diamond. We have measured an ensemble of silicon-vacancy centres across numerous nanodiamonds to have an inhomogeneous distribution of 1.05 nm at 5 K. Individual spectral lines as narrower than 360 MHz were measured in photoluminescence excitation, and correcting for apparent spectral diffusion yielded an homogeneous linewidth of about 200 MHz which is close to the lifetime limit. These results indicate the high crystalline quality achieved in these nanodiamond samples, and advance the applicability of nanodiamond-hosted colour centres for quantum optics applications.

We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy ( ${\rm Si}{{{\rm V}}^{-}}$ ) centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4 K–350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the ${\rm Si}{{{\rm V}}^{-}}$ centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubits in the ground states and propose methods to extend coherence times of ${\rm Si}{{{\rm V}}^{-}}$ qubits.

Abstract: The isolated silicon vacancy is one of the basic intrinsic defects in SiC. We present new experimental data as well as new calculations on the silicon vacancy defect levels and a new model that explains the optical transitions and the magnetic resonance signals observed as occurring in the singly negative charge state of the silicon vacancy in 4H and 6H SiC. [Copyright &y& Elsevier]

An in situ counted ion implantation experiment improving the error on the number of ions required to form a single optically active silicon vacancy (SiV) defect in diamond 7-fold compared to timed implantation is presented. Traditional timed implantation relies on a beam current measurement followed by implantation with a preset pulse duration. It is dominated by Poisson statistics, resulting in large errors for low ion numbers. Instead, our in situ detection, measuring the ion number arriving at the substrate, results in a 2-fold improvement of the error on the ion number required to generate a single SiV compared to timed implantation. Through postimplantation analysis, the error is improved 7-fold compared to timed implantation. SiVs are detected by photoluminescence spectroscopy, and the yield of 2.98% is calculated through the photoluminescence count rate. Hanbury-Brown-Twiss interferometry is performed on locations potentially hosting single-photon emitters, confirming that 82% of the locations exhibit single photon emission statistics.

Abstract: Recently, Goto et al. have discovered anomalous elastic softening due to vacancy in crystalline silicon at very low temperature. To investigate the quantum state of the silicon vacancy, we introduce a cluster model which includes the electron–lattice coupling between electrons and Jahn–Teller distortions together with the Coulomb interaction between electrons. By using the numerical diagonalization method, we take into account of both the nonadiabatic and the correlation effects. We find that the 3-fold orbital degeneracy in the ground state of a silicon vacancy is stable against the Jahn–Teller distortions because of the strong quantum fluctuation due to the nonadiabatic coupling between electrons and Jahn–Teller distortions. The obtained result is a striking contrast to the previous theoretical results within the adiabatic approximation and is consistent with the newly observed experiment. [Copyright &y& Elsevier]

We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy (SiV−) centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4 K–350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the SiV− centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubits in the ground states and propose methods to extend coherence times of SiV− qubits., Physics