the previous one. While it is typically preferred to deposit the metal layer first and include metal markers, our resist thickness and Silicon-under-Nitride negative-tone marker seem to allow sufficient alignment precision for our exploratory capacitors. The metal is deposited using electron beam evaporation, where a reservoir of pure metal is struck with a high-energy electron beam in vacuum, locally heating up the metal to create metal vapor emitted from the reservoir and deposited onto the chip. The metal pattern is defined by exposed areas on the chip that are not covered by the resist. Once the metal deposition is complete, the resist is lifted off from the substrate in solvents (room-temperature trichlorethylene) with the metal layer, leaving the metal pattern only on where it was directly deposited onto the chip itself. We experimented with gold wiring, with Chromium as adhesion layer between Nitride and gold (5nm Cr, then 100nm Au). This configuration has been tested to withstand the KOH etch and subsequent Nanostrip cleaning. We have not yet tested the metal-coated chips with buffered Hydrofluoric acid. With metal wiring, we have preliminary capacitive tuning results for the double-beam photonic crystal, which will be covered in Chapter 8. Also, capability to coat metal can provide future possibilities such as metalized thermal conduction wires or local magnetic field wiring for atoms.
An atom absorbs an oncoming photon by virtue of its constituent electron energy level transitions; provided the photon has a wavelength in resonance with an atomic transition and the majority of atoms repeatedly de-excite to the same initial level, cooling can be achieved. A transition within the tuning range of available lasers and with a strong optical field interaction is chosen to simplify the experimental setup, (the relative interaction strengths of the multiple transitions depend on the orientation of their atomic dipole moment with respect to the polarisation of the input light). On absorbing a photon and receiving a momentum kick of p = h k where h = h/2π, the wavevector k = 2π/ λ and λ is the wavelength of the photon, an electron within the atom is raised to an excited level. Subsequent de-excitation occurs after a time τ , the excited state lifetime of the transition. For Rb 85 , used here, this is τ = 26.63ns. De-excitation emits a photon of similar energy. This emission would cancel the slowing effect if the emitted photon were directed parallel to the input photon, however de-excitation emission is isotropic therefore, time averaged absorption and re-emission pushes the atom in the direction of the photon flux, against its original direction. This process is cyclic and is the basis for atom cooling, whereby a photon is absorbed and spontaneously emitted, it is depicted in Figure 1.1.
scheme allows for phase matching and dramatically increases the nonlinear interaction length between the excitation light and the materials compared to free-space excitation, thus boost the second-harmonic signal. The inver- sion symmetry breaking in monolayer TMDCs brings new opportunities for nonlinear optics especially for SHG, while the efficiency is low due to the sub-nanometer thickness of these materials preventing them from practical applications. The scheme we demonstrate here show that the limited light- matter interaction length could be overcome by waveguide integration, thus opening lots of new opportunities for applications of these 2D TMDCs. In particular, these monolayer TMDCs are suitable for integration with silicon- photonics platform without lattice-mismatch issues, the structure we demon- strate here could serve for second-harmonic source in silicon chip, while sili- con itself does not own second-order nonlinearity due to the symmetric struc- ture. Furthermore, theoretical calculation reveals the coupling and conversion mechanisms in our system, and points out further directions for optimization. The fully scalable platform we demonstrate here brings new opportunities for these 2D TMDCs especially for nonlinear chip-integrated applications.
Quantum photonics is a rapidly developing platform for future quantum network applications. Waveguide-based architectures, in which embedded quantum emitters act as both nonlinear elements to mediate photon–photon inter- actions and as highly coherent single-photon sources, offer a highly promising route to realize such networks. A key requirement for the scale-up of the waveguide architecture is local control and tunability of individual quantum emitters. Here, we demonstrate electrical control, tuning, and switching of the nonlinear photon–photon interaction arising due to a quantum dot embedded in a single-mode nano-photonic waveguide. A power-dependent waveguide transmission extinction as large as 40 2% is observed on resonance. Photon statistics measurements show clear, voltage-controlled bunching of the transmitted light and antibunching of the reflected light, demonstrating the single- photon, quantum character of the nonlinearity. Importantly, the same architecture is also shown to act as a source of highly coherent, electrically tunable single photons. Overall, the platform presented addresses the essential requirements for the implementation of photonic gates for scalable nano-photonic-based quantum information processing.
The cavity QED system consists of an atom coupled to a single mode of the elec- tromagnetic ﬁeld in a cavity. This system is interesting for a number of reasons. To start with, it is a simple quantum mechanical entity, reduced to elementary con- stituents: atoms and photons; thus, it is often possible to predict its behavior with an easily manageable theoretical model. Also, in the regime of strong coupling, the rate of interaction between the atom and the ﬁeld is the dominant parameter in the problem, meaning that dissipative mechanisms do not wash out the coherent evolu- tion of the system. In addition, the cavity output consists of a well-deﬁned, single spatial mode, allowing the photon detection eﬃciency to be far superior to that in free-space, hence making cavity QED an ideal platform for the study of quantum optics. This system also lends itself well to the conversion of stationary qubits of quantum information, as encoded in long-lived atomic states, into “ﬂying” qubits, represented by easily-transported photonic states. This makes it an attractive setup for the implementation of quantum networking and of other quantum information science protocols.
Achieving strong and controllable interactions between atoms and photons at the quantum level has been a central goal in the fields of atomic physics and quantum optics . Historically, the simplicity and the ready availability make atomic systems a platform for observing fundamental quantum phenomena, such as in nonclassical statistics of light emitted by single atoms  and reversible vacuum Rabi oscillations between a single atom and a photon [15, 86, 99]. In many fields of research, including quantum information science, quantum optics, and quantum metrology, interacting systems of atoms and photons are an important resource. With the increasing level of experimental control and the complex interaction that can occur between light and atoms, atomic systems are becoming a platform for investigating new types of many-body phenomena. These phenomena open up new links from quantum optics and atomic physics to quantum information theory and condensed matter. Some of these new areas of research include the self-organization of atoms due to the strong two-way interaction between atom and optical forces [8, 17, 32], and strongly interacting photon gases [12, 80, 111]. The appeal of atomic systems arises from the fact that ultracold atoms are close to an ideal isolated quantum system, ultra-high vacuum keeps atoms isolated from the environment, and the ability to cool atoms to ultracold temperature eliminates inhomogeneity. These properties make neutral atoms a possibility for realizing scalable quantum computers .
A second method for increasing the interaction strength is to minimize the mode area in Eq. (1.2) by more tightly confining the light into a waveguide, as shown in Fig. 1.2(c). This has been used in the nanophotonics community to achieve strong interactions between dielectrics and solid state emitters. While there have been many experiments with atoms coupled to dielectric systems [3, 25], most of them have relied on the high optical Q or large number of atoms rather than the reduce mode area to achieve strong interactions. In the early 2000’s, Hakuta’s group performed experiments coupling the fluorescence of a cloud of atoms to a nanofiber going through the cloud [26, 27]. In the pioneering work by Rauschenbeutal’s group , and now in many other groups [13–15], atoms are optically trapped around a sub-wavelength diameter nanofiber by the optical guided modes of the fiber. This system is convenient for its straightforward loading and cooling scheme, but is still restricted to small mode area since the atoms are trapped in the evanescent tail of the optical mode, resulting in Γ 1D /Γ 0 ≈ 0.03 or R 1.
thanks to the use of slow light, our PCW is 200 times shorter. In comparison to nanophotonic cavities , the approach used here has a conversion efficiency more than one order of magnitude higher. This increase has two major reasons. First, our PCW is capable of hosting most of the 1.3-ps input pulse, which ensures maximum overlap between incident light and pumped Si volume. This assertion is corroborated by Figs. 3(d) and 3(f), which show the PCW output for a Fourier- limited input pulse with a longer duration of 2.3 ps FWHMI. In this case, only part of the input pulse fits in the actuated PCW, resulting in a significantly reduced conversion efficiency. Note that the spatial fraction of the pulse experiencing the mode shift is shorter than the total pulse, which explains the increased bandwidth of the frequency-shifted output [Fig. 3(f)]. Second, despite the use of slow light, the transit time of light through our PCW is still relatively short compared to that of cavities with storage times of more than 15 ps . As a consequence, light absorption by transient free charge carriers is greatly reduced in our PCW.
totally varied for theories . To determine the isospin=1 term of the scattering length, the essential measurement of kaonic deuterium 1 s -state strong-interaction shift and width has been awaited for a long time. There is no evidence of the K − - d X-rays so far due to the low X-ray yield (∼ 10 % of kaonic hydrogen) and the broad width (650–1000 eV predicted by theory) [17, 18]. In order to measure such a low-yield and broad X-ray peaks, a high-eﬃcient and low-background measurement is required. Aimed at the ﬁrst observation of the K − -d X-rays, two experiments are planned at DAΦNE and J-PARC. Table 2 shows the expected parameters of the future experiments.
Devices that harness the surprising properties of quantum systems at scale hold the possibility of revolutionary advances in information technology. Quantum bits, or ‘qubits’ can be prepared in a superposition of classical bit values 0 and 1. Multiple qubits may exist in a combined superposition state that cannot be divided into separate, independent local states. We call this type of correlated superposition an ‘entangled’ state. Algorithms for quantum computers have the ability to solve problems that are intractable with classical hardware, including prime factorization and simulating chemical processes. Furthermore, a quantum communication network that carries qubits instead of bits can take advantage of superposition states to guarantee secure communication. However, because superposition states are fragile and ‘decohere’ under interaction with the environment, building such devices requires exquisite control over many isolated quantum systems. One of the most critical capabilities is the efficient interaction of stationary atomic and flying optical qubits. In this chapter we make a broad survey from high above the field of quantum informa- tion. This survey has a dual purpose: to provide much needed context and motivation for a general audience, and to o↵er an informed perspective on the field for researchers. Such perspective seems timely given the surge of private investment and public interest in quan- tum information technology. With one eye to each of these tasks we describe the separate but related goals of quantum computation and communication, discuss the physics and engineering challenges that must be overcome to achieve these goals, and map a course to these twin destinations in light of recent advances—before finally gliding gracefully back to ground level to outline the work of this thesis and its role in the wider field. The back- ground provided in this chapter is necessarily brief, but it is hoped that the references included provide a comprehensive introduction to the field of quantum information and the need for efficient and coherent atom-light couplers.
the amorphous silicon film improve transmission of electromagnetic radiation, and an enhancement in short- circuit current density and energy conversion efficiency in amorphous silicon p-i-n solar cells is observed. A method of enhancing light trapping by tuning localized surface plasmons through the modification of the local dielectric environment of the particle was reported  in 2009. The surface plasmon resonances can be redshifted by up to 200 nm through the modification of the local dielectric environment of the particles; the optical ab- sorption is increased in an underlying Si wafer fivefold at a wavelength of 1,100 nm and enhances the external quantum efficiency of thin Si solar cells by a factor of 2.3 at this wavelength. The resonance frequency of metal nano-particles depends on the size, shape, particle ma- terial, and refractive index of the surrounding medium . The resonance frequency gets redshifted when the dielectric functions of the surrounding medium increase. Mokkapati et al.  presented their method for opti- mizing the light-trapping efficiency of periodic grating arrays of metal nano-particles for Si solar cell applica- tions. They suggest that the pitch of the grating should be chosen to allow at least one diffraction mode propa- gating outside the escape cone in Si for long wavelength light.
2403, Micro resist technology, Berlin, Germany) was spin-coated onto the Pyrex surface and baked at 90 for 60s. The nano-hole array patterns were written on to the photoresist with the EBL machine (LEO, 1530 e-beam lithography, UWO Nanofab) and the photoresist was subsequently developed (MF-319, Shipley, Marlborough, MA). The process left behind an array of photoresist nano-pillars, which were used as a mask layer during the lift-o¤. A 3-nm thick Ti layer and a 100-nm thick Au layer were deposited in sequence on to the photoresist nano-pillars (electron beam deposition). The 3-nm thick Ti layer served as an adhesion layer between the substrate and the gold …lm. Afterwards, the sample was left in 80 PG Remover (MicroChem Corp., Westborough, MA) and sonicated to facilitate the lift-o¤ process. After lift-o¤, the sample was left in Ti TFTN etchant to remove the Ti con- ductive and adhesion layers. The end result was a nano-hole array structure in a gold …lm on top of the Pyrex substrate.The nano-hole arrays in a 100-nm thick gold …lm on Pyrex substrate with various hole sizes and periodicities was …rst fabricated where nano holes were distributed in a square lattice. A schematic diagram of a nano-hole array structure on pyrex substrate is shown Fig. 2.9a. The holes were circular in cross-section and had 100 nm, 120 nm, and 140 nm hole diameters and 360 nm, 400 nm, and 440 nm periodicities. A scanning electron microscopy (SEM) image of a portion of a fabricated nano-hole structure is shown in Fig. 2.9b. The same method was employed to fabricate nano-hole arrays in metal on Pyrex substrate having a of 287 nm hole size and 440 nm periodicity.
advances in fiber-optic technology that has attracted considerable interest from many researchers around the world. In 1991, J. Russell and his group invented microstructure optical fibers. The fibers were made from silica with a periodic arrangement (in the cross-section) of air-channels running along the full length of the fiber. Photonic crystal fibers (PCFs) can modify the way light is produced, transported and utilized. Supercontinuum generation, four-wave mixing and hollow-core PCF technology may make possible step forwards in science— particularly in medicine and microscopy. [5, 6]
as the most practical realization of PhCs . The introduction of waveguides of narrow width - gen- erally a single row of holes is removed (W1) – al- lowed for the demonstrations of PhC-based devices and slow light in PhC waveguides [4, 5, 6, 7]. These early devices were limited by two factors: (1) strong group velocity dispersion in the slow light region and (2) high propagation loss in the slow light re- gion, both due to operation near the band edge. These limitations were overcome with the advent of dispersion engineered [8, 9, 10, 11] and loss en- gineered waveguides[12, 13], respectively. The re- sultant technological advances led to a wide range of work on PhC devices, including tunable delay lines , adiabatic control of slow light , ultra- small optical switches , enhanced nonlinear ef- fects [17, 18, 19, 20] and enhanced sensitivity spec- trometers .
But it is important to see from Equation (26) that the power spectrum is highly depending on the mean photon number of squeezed vacuum reservoir. The existence of these photons in the reservoir is very important for stimulated emission by the atom. This situation takes place when the atom is initially in the upper electronic energy state and the photon from the reservoir hits the atom which has resonant frequency with atomic transition frequency. Here we have done the mathematical equation behind such conditions which has to be true for the selected model.
A linear waveguide for atoms is all well and good, but for full exploitation of atomic beams we need a way to separate and combine beams, in this way we can generate interferometers. The first all optical beam splitter was realised by Houde and co-workers  using two crossed far from resonance dipole guides to guide rubidium. A vertical beam was used to guide a dropped cloud of atoms from a MOT, with a second beam crossing the first at a slight angle a few mm below the trap. As the atoms fall down the vertical guide they oscillate within the potential from side to side, the crossover region of the two beams must be long enough to allow this oscillation to occur once and permit the atoms to “jump” potentials. The oblique guide is left off initially so that no atoms from the MOT can be caught, it is then turned on when the atoms reach the cross over region of the guides, the sudden potential change from turning the oblique guide on results in a slight momentum kick to the atoms and assists in transferring the atoms across the guides. Transfer of up to 40% was achieved and the separation of the two atom beams was complete after only 10mm.
Most guiding geometries have so far exploited the red-detuned dipole force. Such geometries allow the use of simple Gaussian laser beams but, because the atoms are attracted into regions of high optical intensity, the guiding forces are accompanied by a signiﬁcant scattering force. Blue-detuned optical guiding, where the light frequency is tuned above resonance, has the advantage that the atoms are then restricted to regions of intensity minima, and perturbations induced by the light ﬁeld are thus minimized. Blue-detuned guiding of a cold atomic beam along a hollow, low-order Laguerre–Gaussian light beam has already been reported [5, 6], as has the guiding of cold atom clouds dropped from magneto-optical traps (MOTs) into hollow beams generated using axicon lenses  and hollow optical ﬁbres . These various schemes each have their merits, but these forms of beam generation are not true propagating modes and may show a signiﬁcant change in transverse beam proﬁle with propagation. The frequency detuning is also a key parameter, and the near-resonant guiding of Song et al.  is accompanied by signiﬁcant radiation pressure, which can levitate or push the atomic cloud and which causes heating of up to 15 mK. When the detuning exceeds 10 GHz and the cloud is cooled in a molasses cycle, however, extended guiding can occur with relatively little heating .
Several factors concerning the optimized design of PhC(PhQ)-based LEDs and their eﬀect on the enhancement of light extraction have been discussed. These include the lattice types, the ratio of cylinder radius and lattice constant, the DOS from a dispersion relation, the thickness of a PhC (PhQ) layer, and the position in which a PhC (PhQ) could be inserted. Some rules of practical implementation are oﬀered for high-eﬃciency LEDs. Beneﬁts of Archimedean tilings known as PhQs were presented, and numerical quantitative comparisons in the relative enhancement of the light extraction based on the 3D FEM were drawn with optimized parameters of improving extraction eﬃciency. With the use of an optimized periodic pattern of the (4, 8 2 ) Archimedean lattice, an increase of ∼ 2.8 in the extraction eﬃciency of the LED is expected theoretically. The light extraction for the incorporation of the Archimedean lattice under the optimized parameters exhibits about 1.6 and 1.9 times higher extraction than that of the square and triangular lattices, respectively. The Archimedean tiling pattern provides a favorable consideration of 2D-PhC in light extraction from LEDs.