An ever increasing effort has been devoted over the years to develop techniques for manipulating light in optical devices. Electromagnetic induced transparency (EIT) is one of these techniques that has recently led to an astonishing control on light wave propagation in ultracold clouds of alkali atoms. EIT may be employed to realize a photonic band gaps that are controllable through the parameters of an external standing light wave pattern [1]. Such gaseous approaches are not however suitable for on-chip implementation. Early work on control over photonic band-gap comprises, e.g., structures built from the periodic complex susceptibility of quantum well excitons whose optical properties can be dynamically modified through the Stark effect. Other interesting proposals to control photonic band-gaps in semiconductor heterostructures have been brought forward and where control over the band-gap is achieved through EIT in conduction intersubband transitions of a n-doped quantum well. EIT effects have also been observed in a class of solid materials exhibiting defect states, following either familiar or less familiar schemes, and among which presodimium doped Y2SiO5 and diamond containing nitrogen vacancies (N-V) color centers are perhaps the most ubiquitous ones. Color centers in diamond, in particular, have attracted over the past few years a renewed interest for their potential as single-photon sources and are attractive qubit candidates as they behaves a bit like an atom trapped in the diamond lattice. These centers can have extremely long-lived spin coherence because the diamond lattice is composed primarily of 12C, which has zero nuclear spin. In addition, N-V color centers also have interesting optical properties as they exhibit a configuration with two ground state levels connected to a common excited state by optical transitions of moderate strength leading to a lambda-type level configuration required for the observation of EIT [2,3]. This has been exploited to devise a novel photonic band-gap mechanism [4]. We here study the propagation of a very week optical pulse in the band-gap region of N-V diamond crystals. Our calculations show that adopting realistic parameters, as taken from recent experiments on coherent population trapping in N-V color centers, nearly complete reflectivities can be attained in a mm long diamond sample. This occurs when most probe frequency components lie inside the band-gap, yielding instead controllable loss and distortion as the incident probe pulse falls outside the gap. The relevant photonic band-gap may be all optically controlled while its well developed structure is seen to arise from the reduced values of residual absorption in the EIT region. [1] M. Artoni et al., Phys. Rev. Lett. 96, 073905 (2006). [2] C. Wei et al., Phys. Rev. A 60, 2540 (1999). [3] P. Hemmer, et al.,Opt. Lett. 26, 361 (2001). [4] Q.-Y. He, et al., Phys. Rev. B 73, 195124 (2006).
An ever increasing effort has been devoted over the years to develop techniques for manipulating light in optical devices. Electromagnetic induced transparency (EIT) is one of these techniques that has recently led to an astonishing control on light wave propagation in ultracold clouds of alkali atoms. EIT may be employed to realize a photonic band gaps that are controllable through the parameters of an external standing light wave pattern [1]. Such gaseous approaches are not however suitable for on-chip implementation. Early work on control over photonic band-gap comprises, e.g., structures built from the periodic complex susceptibility of quantum well excitons whose optical properties can be dynamically modified through the Stark effect. Other interesting proposals to control photonic band-gaps in semiconductor heterostructures have been brought forward and where control over the band-gap is achieved through EIT in conduction intersubband transitions of a n-doped quantum well. EIT effects have also been observed in a class of solid materials exhibiting defect states, following either familiar or less familiar schemes, and among which presodimium doped Y2SiO5 and diamond containing nitrogen vacancies (N-V) color centers are perhaps the most ubiquitous ones. Color centers in diamond, in particular, have attracted over the past few years a renewed interest for their potential as single-photon sources and are attractive qubit candidates as they behaves a bit like an atom trapped in the diamond lattice. These centers can have extremely long-lived spin coherence because the diamond lattice is composed primarily of 12C, which has zero nuclear spin. In addition, N-V color centers also have interesting optical properties as they exhibit a configuration with two ground state levels connected to a common excited state by optical transitions of moderate strength leading to a lambda-type level configuration required for the observation of EIT [2,3]. This has been exploited to devise a novel photonic band-gap mechanism [4]. We here study the propagation of a very week optical pulse in the band-gap region of N-V diamond crystals. Our calculations show that adopting realistic parameters, as taken from recent experiments on coherent population trapping in N-V color centers, nearly complete reflectivities can be attained in a mm long diamond sample. This occurs when most probe frequency components lie inside the band-gap, yielding instead controllable loss and distortion as the incident probe pulse falls outside the gap. The relevant photonic band-gap may be all optically controlled while its well developed structure is seen to arise from the reduced values of residual absorption in the EIT region. [1] M. Artoni et al., Phys. Rev. Lett. 96, 073905 (2006). [2] C. Wei et al., Phys. Rev. A 60, 2540 (1999). [3] P. Hemmer, et al.,Opt. Lett. 26, 361 (2001). [4] Q.-Y. He, et al., Phys. Rev. B 73, 195124 (2006).
Inhomogeneously broadened optical transitions of nitrogen-vacancy centers in diamond may be employed to attain fully developed photonic band-gap structures with negligible absorption via coherent optical nonlinearities. For realistic material parameters, the resulting band gap may be tuned via the coupling field to acquire reflectivities very close to unity and sufficiently large bandwidths. We anticipate that this can be used to optically control with remarkable experimental simplicity the reflected and transmitted parts of an incident light pulse.
Controlling quantum coherence in light‐matter interaction is a key step for advanced ultra‐fast and quantum information technology. We theoretically consider a scheme to realize all‐optically induced photonic band gaps based on a standing wave electromagnetically induced transparency configuration which can be implemented with nitrogen‐vacancy color centers in diamond. For realistic material parameters the resulting band‐gap may be tuned via the coupling field to acquire reflectivities very close to unity and sufficiently large bandwidths.
The nitrogen-vacancy (NV) center in diamond has garnered great interest over the past decade as its electronic spin shows promise as a quantum bit (qubit) and nanoscale sensor. Consisting of a substitutional nitrogen adjacent to a vacant site within the carbon lattice of diamond, this defect exhibits millisecond-long spin coherence times extending beyond room temperature, spin-dependent optical addressability, coupling to intrinsic and nearby nuclear spins, and it can be controlled and manipulated through electrical, magnetic, and optical means. In particular, at cryogenic temperatures (T < 25 K), the NV center's excited state becomes sharp and optically resolvable, providing a solid-state quantum optical testbed. In this thesis, I describe several experiments that explore this quantum optical interface to facilitate the development of a photonic network of single spins linked and controlled by light. We begin by exploring how electric fields tune the orbital levels within the NV center through the DC Stark effect, finding a surprising photo-induced field that aids in the ability to tune multiple NV centers' optical transitions to degeneracy. We then develop techniques to fully control the spin state of the NV center by coupling through a lambda system, an energy configuration consisting of two lower levels coupled to one of higher energy. When a lambda system is optically driven, the spin becomes trapped in a dark state, or the eigenstate of the system that is not coupled to the light fields through destructive interference, forming the basis for the various types of control demonstrated. We demonstrate arbitrary-basis initialization and readout of the spin state through coherent population trapping, as well as the ability to rotate about any arbitrary basis through stimulated Raman transitions. Combining these techniques, we measure the NV center's spin coherence through a completely optical measurement. We then extend these lambda system techniques to adiabatically move the dark state in trajectories around the Bloch sphere. Such trajectories accumulate a quantum mechanical phase that depends only on the geometry of the path enclosed, not on the energetics or time of the interaction. We characterize the interaction, measure this phase, known as Berry phase, and explore the limits of its control and resilience to noise. Finally, we demonstrate another all-optical control technique that uses strong ultrafast pulses of light to transfer the spin between the ground and excited states, deriving spin manipulation from the excited state dynamics. This technique also provides time-resolved spectroscopy of the excited state and its various decay and decoherence mechanisms. These experiments advance the progress toward the development of photonic networks coupling and controlling defects through light-matter interactions.
Luminescent lattice defects (so called “color centers”) in diamond provide a robust, solid-state architecture for exploring quantum optics, with many facilitating direct access to highly coherent electron and nuclear spins. The past two decades have seen tremendous advances in our ability to prepare and control the quantum states of these atom-like systems. For instance, demonstrations that leverage the diamond nitrogen vacancy (NV–) center as a spin-photon interface have included the generation of indistinguishable photons, a quantum bit memory exceeding 1 second, entanglement of two distance solid-state qubits, and deterministic long distance quantum teleportation. While diamond color centers are an attractive platform for scalable quantum information processing, the diamond solid-state matrix, by its very nature, inhibits efficient photon collection into either free-space or fiber-optical systems. Due to its large refractive index, emitted photons are inevitably trapped within the diamond crystal by total internal reflection, limiting count rates and overall scalability of information processing via quantum optical protocols. To this end, there has been significant progress towards integrating individual diamond color centers within well-defined radiation channels: namely, those provided by monolithic diamond nanophotonic networks. Currently, on-chip low loss (~ few db/cm) diamond waveguide networks are available, as well as key passive photonic elements like micron scale ring and disk resonators and photonic crystal cavities, with high optical quality (Q) factors. Specifically, we recently demonstrated a scalable ‘angled-etching’ nanofabrication method for realizing nanophotonic networks starting from bulk single-crystal diamond substrates (MJ Burek et al., Nano Letters 2012, MJ Burek et al., Nat Comm. 2014). Angled-etching employs anisotropic oxygen-based plasma etching at an oblique angle to the substrate surface, resulting in suspended optical structures with triangular cross-sections. Using this approach, we demonstrated high Q-factor (> 10^5) optical nanocavities fabricated in bulk single-crystal diamond, operating over a wide wavelength range (visible to telecom). Beyond isolated photonic devices, we have further developed free-standing angled-etched waveguides which efficiently route photons between diamond optical nanocavities, while maintaining physical support through attachment to the bulk substrate. Although on-chip diamond nanophotonics realized by angled-etching continue to mature, efficient off-chip optical coupling schemes which provide near seamless transition of photons on-chip into commercial optical fibers remain an outstanding challenge. This is especially pertinent in applications involving single photons, such as quantum optics with diamond color centers. Herein, we demonstrate a high efficiency fiber-optical interface with aforementioned on-chip diamond nanophotonic networks, achieving > 90% power coupling at both telecom and visible wavelengths. The coupling scheme utilizes a single mode optical fiber, with one end fabricated into a conical taper, to adiabatically transition guided light between on-chip tapered diamond waveguides and off-chip optical fiber networks. Additionally, we develop techniques to robustly pigtail single-mode fibers with diamond waveguide couplers, yielding a packaged technology that may potentially enable deployment in harsh environments, including vacuum, sub-Kelvin cryogenics, or even liquid/biological environments. With these newly developed optical integration schemes, single-crystal diamond is now a viable integrated nanophotonics platform, servicing a range of applications, from non-linear optics and chemical sensing, to quantum science and cavity optomechanics.
Development of quantum information processing requires realization of solid state structures able to manipulate light or matter quantum bits. One of the promising candidates for been active elements of such solid-state platform are color centers in diamond. The most famous nitrogen-vacancy color center has number of attractive features and found a lot of applications in sensing and imaging. Still, it has number of considerable disadvantages, among which it sensitivity to the surface damages and thus its incompatibility with nanostructures. On another side implementation of nano- and micro- structures enabled considerable progress in manipulation of light quanta. In particular photonic crystal cavities allowed to realize strong coupling of cavity and spin system. This led to demonstration of efficient light collection and realization of simple quantum gates with artificial or real atoms. Novel color centers such as silicon-vacancy or germanium-vacancy color center due to inversion symmetry of the electron structure are not sensitive to the surface damages and presence of surface nearby. Thus, those are perfect candidates for been combined with photonic crystal structures. Novel technologies enabled growing of the nanodiamonds of ultra-small size having well-defined color center inside. Along with techniques to position those precisely on the nano- and micro structures these achievements opened opportunity to integrate high-fines photonic-crystal cavities with the germanium-vacancy containing nanocrystals thus forming fully solid-state platform for quantum manipulation of light. In my talk I will describe our progress towards realization of this ambitious goal.