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Quantum emitters are an integral component for a broad range of quantum technologies, including quantum communication, quantum repeaters, and linear optical quantum computation. Solid-state color centers are promising candidates for scalable quantum optics due to their long coherence time and small inhomogeneous broadening. However, once excited, color centers often decay through phonon-assisted processes, limiting the efficiency of single-photon generation and photon-mediated entanglement generation. Herein, we demonstrate strong enhancement of spontaneous emission rate of a single silicon-vacancy center in diamond embedded within a monolithic optical cavity, reaching a regime in which the excited-state lifetime is dominated by spontaneous emission into the cavity mode. We observe 10-fold lifetime reduction and 42-fold enhancement in emission intensity when the cavity is tuned into resonance with the optical transition of a single silicon-vacancy center, corresponding to 90% of the excited-state energy decay occurring through spontaneous emission into the cavity mode. We also demonstrate the largest coupling strength (g/2π = 4.9 ± 0.3 GHz) and cooperativity (C = 1.4) to date for color-center-based cavity quantum electrodynamics systems, bringing the system closer to the strong coupling regime.

We investigate the influence of exciton-phonon coupling on the dynamics of a strongly coupled quantum dot-photonic crystal cavity system and explore the effects of this interaction on different schemes for nonclassical light generation. By performing time-resolved measurements, we map out the detuningdependent polariton lifetime and extract the spectrum of the polariton-to-phonon coupling with unprecedented precision. Photon-blockade experiments for different pulse-length and detuning conditions (supported by quantum optical simulations) reveal that achieving high-fidelity photon blockade requires an intricate understanding of the phonons' influence on the system dynamics. Finally, we achieve direct coherent control of the polariton states of a strongly coupled system and demonstrate that their efficient coupling to phonons can be exploited for novel concepts in high-fidelity single-photon generation.

Diamond hosts optically active color centers with great promise in quantum computation, networking, and sensing. Realization of such applications is contingent upon the integration of color centers into photonic circuits. However, current diamond quantum optics experiments are restricted to single devices and few quantum emitters because fabrication constraints limit device functionalities, thus precluding color center integrated photonic circuits. In this work, we utilize inverse design methods to overcome constraints of cutting-edge diamond nanofabrication methods and fabricate compact and robust diamond devices with unique specifications. Our design method leverages advanced optimization techniques to search the full parameter space for fabricable device designs. We experimentally demonstrate inverse-designed photonic free-space interfaces as well as their scalable integration with two vastly different devices: classical photonic crystal cavities and inverse-designed waveguide-splitters. The multi-device integration capability and performance of our inverse-designed diamond platform represents a critical advancement toward integrated diamond quantum optical circuits.

A two-level atom can generate a strong many-body interaction with light under pulsed excitation [1][2][3] . The best known e ect is single-photon generation, where a short Gaussian laser pulse is converted into a Lorentzian single-photon wavepacket 4,5 . However, recent studies suggested that scattering of intense laser fields o a two-level atom may generate oscillations in two-photon emission that come out of phase with the Rabi oscillations, as the power of the pulse increases 6,7 . Here, we provide an intuitive explanation for these oscillations using a quantum trajectory approach 8 and show how they may preferentially result in emission of two-photon pulses. Experimentally, we observe the signatures of these oscillations by measuring the bunching of photon pulses scattered o a two-level quantum system. Our theory and measurements provide insight into the re-excitation process that plagues 5,9 ondemand single-photon sources while suggesting the possibility of producing new multi-photon states.We begin by considering an ideal quantum two-level system that interacts with the outside world only through its electric dipole moment µ (ref. 10). Suppose the system is instantaneously prepared in the superposition of its ground |g and excited |e stateswhere P e is the probability of initializing the system in |e . From this point, spontaneous emission at a rate of Γ governs the remaining system dynamics and a single photon is coherently emitted with probability P e , while no photon is emitted with probability 1 − P e . As detected by an ideal photon counter, this results in the photocount distributionwhere P n is the probability to detect n photons in the emitted pulse. It is on this principle that most indistinguishable single-photon sources based on solid-state quantum emitters operate 4,5 .A popular mechanism for approximately preparing |ψ i is the optically driven Rabi oscillation 4,11 . Here, the system is initialized in its ground state and driven by a short Gaussian pulse from a coherent laser beam (of width τ FWHM ) that is resonant with the |g ↔ |e transition. Short is relative to the lifetime of the excited state τ e = 1/Γ to minimize the number of spontaneous emissions that occur during the system-pulse interaction 5,9 . As a function of the integrated pulse area, that is, A = dtµ · E(t)/ , where E(t) is the pulse's electric field, the system undergoes coherent oscillations between its ground |g and excited |e states. For constant-area pulses of vanishing τ FWHM /τ e , the final state of the system after interaction with the laser field is arbitrarily close to the superpositionwhere φ is a phase set by the laser field. Examining P e (A) (Fig. 1a dotted line), we see Rabi oscillations that are perfectly sinusoidal, with the laser pulse capable of inducing an arbitrary number of rotations between |g and |e . Because |ψ f (A) looks very much like |ψ i for arbitrarily short pulses, it is commonly assumed that the photocount distribution P n always has P 1 P n>1 . However, we will use a quantum trajectory appro...

The study of light-matter interaction at the quantum scale has been enabled by the cavity quantum electrodynamics (CQED) architecture, 1 in which a quantum two-level system strongly couples to a single cavity mode. Originally implemented with atoms in optical cavities, 2, 3 CQED effects are now also observed with artificial atoms in solid-state environments. 4-6Such realizations of these systems exhibit fast dynamics, which makes them attractive candidates for devices including modulators and sources in high-throughput communications. However, these systems possess large photon out-coupling rates that obscure any quantum behavior at large excitation powers. Here, we have utilised a self-homodyning 7 interferometric technique that fully employs the complex mode structure of our nanofabricated cavity [8][9][10] to observe a quantum phenomenon known as the dynamic Mollow triplet. 11We expect this interference to facilitate the development of arbitrary on-chip quantum state generators, thereby strongly influencing quantum lithography, metrology, and imaging.The crowning achievement of quantum optics has been to develop a complete theory for the phenomenon of resonant light scattering from a quantized matter system. Beyond providing closure to debates over the nature of light, this theory has enabled observations of uniquely quantum spectacles such as photon antibunching, 4,12 indistinguishable quantum interference, 5,13 and the Mollow triplet. 14, 15The addition of nanoscale resonators to the quantum scattering problem has provided a new frontier in our quest to mould the flow of light. 4-6Here, our reported innovation centres on the investigation of resonant light scattering from a quantum nonlinearity (quantum dot [QD]) strongly coupled to a photonic crystal [PC] cavity. This strong coupling allows for quantum-coherent energy exchange between the resonator's quantized light field and the QD's excitonic field, leading to the formation of light-matter entangled states known as polaritons. 16-18Evidence for the system's strong coupling is provided from the clean avoided-crossing spectra in Fig. 1a. The relative positions of the emission peaks are determined by the transient energies of the Jaynes-Cummings (JC) ladder 19 (Fig. 1b). As the two polaritonic peaks transition of the coupled QD-cavity system obtained when tuning the QD resonance through the cavity mode. By fitting profiles from these spectra, we extract the cavity energy decay rate κ = 2π · 15 GHz and the coherent coupling rate g = 2π · 11 GHz. b, Transient energies for climbing the JC-ladder rung by rung for the first, second and third rung as solid, dashed and dotted lines, respectively. Transitions from upper and lower polaritons are colour coded in red and blue, respectively. c,d, Spectra of the coupled QD-cavity system taken at a QD-cavity detuning of ∆σa = −85 pm and an excitation power of roughly 15 nW/nm, showing QD-like polaritonic emission (highlighted by grey box) on top of (c) a Lorentzian resonance and (d) a Fano resonance. In both cases, ...

Group-IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. Future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group-IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV − ) center, conventional 1 arXiv:1910.14165v1 [cond-mat.mes-hall] 30 Oct 2019 site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV − centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.Keywords diamond color centers, tin-vacancy center, CVD growth, ion implantation Group-IV color centers in diamond have emerged as promising candidates for optically active, solid-state spin qubits. 1-4 These color centers are comprised of a split vacancy in the diamond lattice and an interstitial group-IV atom. The inversion symmetry of this structure provides group-IV color centers beneficial properties such as insensitivity to electric field fluctuations to first order and high Debye-Waller factors. 5 These color centers also possess long-lived electron spins that can be harnessed as quantum memories. 6-8 All of these characteristics make group-IV color centers well suited to interface optical photons in nanophotonic platforms for applications in quantum networks.An outstanding challenge in implementing these color centers in scalable applications is their generation. The two most common methods of group-IV color center generation are ion implantation and synthesis. Ion implantation facilitates site-controlled generation of color centers by using either a mask 9,10 or focused ion beam (FIB). 11,12 However, the quality of ion-implanted emitters is often degraded by the large amount of damage introduced during implantation. 4 Synthesis techniques such as high-pressure high-temperature (HPHT) growth and chemical vapor deposition (CVD) growth often yield higher quality, more stable emitters with lower inhomogeneous broadening than ion implantation. [13][14][15][16] Unfortunately, synthesis techniques do not enable site-controlled generation. A better color center generation method is severely lacking.

We demonstrate a new approach for engineering group IV semiconductor-based quantum photonic structures containing negatively charged silicon-vacancy (SiV − ) color centers in diamond as quantum emitters. Hybrid SiC/diamond structures are realized by combining the growth of nanoand micro-diamonds on silicon carbide (3C or 4H polytype) substrates, with the subsequent use of these diamond crystals as a hard mask for pattern transfer. SiV − color centers are incorporated in diamond during its synthesis from molecular diamond seeds (diamondoids), with no need for ionimplantation or annealing. We show that the same growth technique can be used to grow a diamond layer controllably doped with SiV − on top of a high purity bulk diamond, in which we subsequently fabricate nanopillar arrays containing high quality SiV − centers. Scanning confocal photoluminescence measurements reveal optically active SiV − lines both at room temperature and low temperature (5 K) from all fabricated structures, and, in particular, very narrow linewidths and small inhomogeneous broadening of SiV − lines from all-diamond nano-pillar arrays, which is a critical requirement for quantum computation. At low temperatures (5 K) we observe in these structures the signature typical of SiV − centers in bulk diamond, consistent with a double lambda.These results indicate that high quality color centers can be incorporated into nanophotonic structures synthetically with properties equivalent to those in bulk diamond, thereby opening opportunities for applications in classical and quantum information processing.