Nonlinear optical processes are essential for modern photonics and they are possible mostly when light is produced by a high-power laser. However, nonlinear effects of non-optical origin, such as those observed in acoustical and mechanical systems, are many orders of magnitude stronger than optical nonlinearities, and therefore they can be induced with energy that is much lower than that of a laser pulse. Here, we experimentally confirm our theoretical prediction of the possibility to convert giant acoustic and capillary wave nonlinearities into optical signals, thereby effectively reproducing the result of a conventional nonlinear-optical interaction. We excite highly nonlinear capillary Faraday waves on the surface of a thin layer of ethanol and we reflect a beam of low-power, incoherent light from these waves to produce an optical frequency comb. Our results can be used in many areas of photonics, including new classes of biomedical sensors that do not rely on high laser powers.
Nanodiamonds containing the Nitrogen-vacancy (NV) centre are emerging as a unique platform for nanoscale sensing in biological systems. There is particular interest in the capability of sensing subcellular changes of magnetic and electrical fields, temperature, and pressure. However, the sensitivity of such nanodiamond particles with NV centre as a probe is highly dependent on the relative location and polarisation of the NV centre to the bulk of the particle. Here we show the optical scattering from an NV centre in a nanodiamond as a function of position and orientation within the nanodiamond. The scattering fields are obtained by using the recently developed robust non-singular surface integral equation method.1, 2 Our results highlight a new pathway to nanodiamond characterisation which may be useful in teasing out the various effects of surface morphology, surface termination, and formation details, which ultimately may benefit the optimisation of diamond production for nanoscale biosensing applications.
Nanoscale thermometry of biological systems offers new insights into cell metabolism at a sub-cellular scale. Currently, there is no way in which we can achieve high resolution temperature sensing on these systems without the use of foreign materials such as biological markers. Using rare-earth doped tellurite glass as a platform for thermometry, we report micron scale scale temperature sensing via confocal scanning microscopy. We demonstrate this technique by monitoring the cooling from a water droplet and report a net temperature change of 7.04K with a sensitivity of 0.12K. These results pave the way for “marker free” micron scale temperature sensing in biological systems.
The nitrogen-vacancy (NV) centre in diamond is a perfect candidate for quantum sensing applications applied to numerous fields of science. Past studies improved the sensitivity of diamonds containing NV centres by increasing their density or prolonging their coherence time. However, few studies discussed the effects of other defects inside the diamond crystal on the sensitivity of the NV centres. In this study, we demonstrated the implication of single substitutional nitrogen defects on the fluorescence emission, charge state stability, coherence time and sensitivity of the NV centres. We found that there is an optimal concentration of nitrogen defects that allows diamond samples to have a high-density of NV centres and high fluorescence without significantly affecting the coherence time. This results will inform the correct choice of diamond characteristics for current and future quantum sensing applications with the NV centres.
Achieving higher resolution scales in optical microscopy allow a more rigorous investigation into the detailed components of cell systems. This higher resolution is typically achieved through super-resolution techniques utilizing methods inside the wave-like nature of light such as point spread function shaping and fluorophore switching. We wish to leverage both particle-like and wave-like natures of light to make a diffraction unlimited protocol. Our protocol uses the well known Hanbury Brown and Twiss (HBT) apparatus in combination with a customized second-order cross-correlation protocol. By performing least squares fitting of the HBT and intensity measurements we obtain diffraction unlimited localization for two particles of unknown relative brightness from few measurement locations. Our results show super-resolution enhancement by an order of magnitude after 5000 detection lifetimes.
Techniques of optical superresolution imaging are vital for uncovering the complex dynamics of biochemistry in cellular environments. However the practical resolution for superresolution imaging is limited by the increased photon budget for superresolution, compared with conventional microscopy. For this reason it is important to determine the optimal methods for analysing all of the incoming information. Most approaches to microscopy use only the wave-like properties of light, but the particle-like nature of light provides extra information that is normally inaccessible and can be used to increase imaging resolution. Here we theoretically study the localisation of quantum emitters using higher-order quantum correlation functions to understand the resolution that is practically achievable for bio-imaging tasks. We show explicit imaging results for varying number of emitters as a function of correlation order to illustrate the necessary tradeoffs between imaging resolution and acquisition time.
The UV-C band ultraviolet light irradiation is one of the most commonly used ways of disinfecting water contaminated by pathogens such as bacteria and viruses. Sonoluminescence, the emission of light from acoustically-induced collapse of air bubbles in water, is an efficient means of generating UV-C light. However, because a spherical bubble collapsing in the bulk of water creates isotropic radiation, the fluence of the generated UV-C radiation is insufficient for disinfection. Here, we theoretically demonstrate that we can create a UV light beam from aspherical air bubble collapse near a gallium-based liquid-metal microparticle. The beam is perpendicular to the metal surface and is caused by the interaction of sonoluminescence light with UV plasmon modes in the metal. We calculate that such beams are capable of generating UV-C fluences exceeding 10mJ/cm2, which is sufficient to irreversibly inactivate 99.9% of pathogens in water with the turbidity of more than 5NTU.
The optomechanical interaction between photonic and phononic waves in micron scale devices is increasingly becoming important for ultrasensitive force and mass sensing applications. Diamond is an exception material for the coupling of optical and mechanical modes because of the low absorption in visible spectrum and high mechanical modulus. To generate optomechanical coupling it is essential to achieve mechanical resonances in the GHz range. Previous work has shown that it is possible to achieve acoustic band gaps at such high frequencies by high-order band gaps which exploit periodic structures with novel topologies. In this work we investigate how the topology and geometry of the periodic structures influence the photon and phonon mode-confinement as well as the optomechanical coupling. By changing the topology and geometry of a unit cell structure based the properties of the targeted Bloch mode, both the resonant mode frequencies and the bandwidth can be tuned. The design method is able to achieve structures with quite large gap sizes for out-of-plane wave, in-plane wave, and the combined waves, which introduces more controllable mechanical modes in the cavity designs in diamond for strong coupling effects.
This work reports nanodiamond-silk membranes as an optical platform for biosensing and cell growth applications. The hybrid structure was fabricated through electrospinning and mimics a 2D scaffold with high porosity. The negatively charged nitrogen vacancy (NV-) centres in diamond exhibits optically detected magnetic resonance (ODMR), which enables sensing of temperature variations. The NV- centre, as reported in literature, provides a shift of 74 kHz in the ODMR frequency per degree rise in temperature. For our hybrid membranes, we have however observed that the embedded NV- centre provide a greater shift of 95±5 kHz/K in the ODMR frequency. This higher shift in the frequency will result in improved temperature sensitivity enabling the tracking of thermal variations in the biologically relevant window of 25-50 ºC. The thermal conductivity of silk and diamond-silk hybrid will be explored to investigate this enhanced temperature sensing ability of diamond. The hybrid diamond-silk membranes are found to be hydrophilic with a contact angle of (65±2)º. The biocompatibility of the membranes is tested both in vitro in skin keratinocyte (HaCaT) cells and in vivo in a live mouse wound model. The membranes did not induce any toxicity to the cell growth and survival. Moreover, we observed resistance towards the growth and attachment of bacteria.
High precision magnetometry is important for a range of applications from the monitoring of biologically generated magnetic fields (e.g. magnetoencephalography and magnetocardiography), to navigation in GPS denied environments, to the detection of gravitational waves. Diamond containing the negatively-charged nitrogen vacancy colour centre (NV-) has emerged as a powerful room-temperature sensing solution. Here we explore NV- centres as a laser medium for a new form of magnetometry: laser threshold magnetometry (LTM). LTM works by placing NV- inside an optical cavity and uses the coherent laser output as a potentially more sensitive readout channel than is possible using conventional (incoherent) optically detected magnetic resonance. Here we show progress towards LTM with diamond. We show twolaser excitation and stimulated emission in free space, and report progress towards diamond-cavity experiments. Our studies highlight the need for different NV- optimisation for laser applications, rather than those conventionally used for quantum information applications
We demonstrate fabrication and characterizations of intrinsically magneto-sensitive fiber with potential applications as a high-efficiency remote magnetic field sensing platform. The fibre was fabricated using lead-silicate glass and the rod-intube fibre drawing technique. The thin glass rod of ~1 mm diameter was first coated with nitrogen-vacancy (NV) centreenriched diamond particles of ~1 μm diameter, and subsequently inserted into the glass outer tube. This rod-in-tube assembly was drawn down to fibre, with the diamond particles distributed at the fused interface between rod and tube. We experimentally coupled 532 nm continuous-wave laser into a 30-cm-length fibre piece from the fibre endface, and examined the photoluminescence (PL) properties of the fibre from both the side of the fibre and the output end of the fibre. PL mapping results showed that the glass-embedded NV emitters showed bright and photostable fluorescence, demonstrating characteristic NV centre zero phonon line emission. Moreover, the mapping result obtained at the output end of fibre indicated that the transmitted NV fluorescence was coupled into the propagation modes of the fibre. By using optically detected magnetic resonance (ODMR) from the NV ensemble along the fibre, we demonstrate detection of local magnetic fields via longitudinal excitation and side collection. Based on the current light transmission and collection configuration, the hybrid diamond-glass optical fibre sensor demonstrated a shot noise-limited DC magnetic field sensitivity of 3.7 μT/√Hz at room temperature. Our results open the possibility of robust, field-deployable fibre optical magnetometry.
The direct write of photonic elements onto substrates presents opportunities for rapid prototyping and novel sensing architectures in domains inaccessible to traditional lithography. In particular, focussed electron beam induced deposition (FEBID) of platinum is a convenient technology for such direct-write applications with the advantage of relatively controlled deposition parameters and sub-10 nm resolution. One issue for FEBID of platinum is that the precursor gas contains a relatively high carbon content, which in turn leads to carbonaceous deposits in the final structure. Here we explore the creation of plasmonic nanoantennae using FEBID platinum. We compare as-deposited and annealed antenna with heights of 40 nm and 56 nm, showing the effect of annealing on the carbon concentration and hence the optical properties. These results are compared with modelling using Mie scattering theory. Our results show that FEBID platinum is a useful material for the direct-write of plasmonic nanoantenna.
We present a new approach to planar photonic interconnects based on spatial adiabatic passage between thin ridge silicon waveguides. Our approach provides robust coupling between arbitrary pairs of well-separated waveguides across a single chip, potentially bypassing intermediate waveguides and structures. This new technique presents opportunities for waveguide routing and device topologies that cannot be achieved using traditional evanescent coupling, while remaining compatible with conventional CMOS fabrication techniques.
We report the generation of sub-surface nanouidic channels from single crystal diamond. To make the channels, we used a combination of ion-beam induced damage and annealing to create a buried, etchable graphitic layer in the diamond. Either laser or focussed ion-beam milling was then used to connect to that layer, and subsequent electro-chemical etching used to remove the graphitic material. The channels had dimensions 100-200 nm thick, 100 μm wide and 300 μm long, which have a total volume around 3 pL; and were around 3 μm below the diamond surface.
The Jaynes-Cummings-Hubbard model describes a network of interacting atom-cavity systems. In this model
the photons can hop between cavities effecting a tunneling interaction, and the Jaynes-Cummings interaction
gives rise to an onsite interaction. This model forms a bridge connection between condensed matter physics and
quantum optics. Here we review the physics underpinning this model, properties of Jaynes-Cummings-Hubbard
systems, the requirements on systems for realizing this model, and some of the progress to date.
Recent advances in the production of high-purity synthetic diamonds have made diamond an accessible host material for
applications in present and future optoelectronic and photonic devices. We have developed a scalable process for
fabricating photonic devices in diamond using reactive ion etching (RIE) and photolithography as well as using ion
implantation to provide vertical confinement. Applying this we have demonstrated a few-moded waveguide with a large
cross section for easier coupling to optical fibre. We present our work towards in-plane coupling to diamond waveguides
and consequently characterisation of these waveguides. We also examine the application of diamond waveguides to other
photonic applications for achieving light confinement in a subwavelength cavity site using a slot-waveguide design. Such
cavities may be used to enhance photon-emission properties of a built-in diamond colour centre and to achieve strong
light-matter interactions on the single-quantum level necessary for quantum information technology. Using single
cavities as building block, we also show that these structures can be suitably coupled to form one-dimensional coupled-resonator
array.
Nitrogen-vacancy centers in diamond typically have spin-conserving optical transitions, a feature which allows
for optical detection of the long-lived electronic spin states through fluorescence detection. However, by applying
stress to a sample it is possible to obtain spin-nonconserving transitions in which a single excited state couples to
multiple ground states. Here we describe two-frequency optical spectroscopy on single nitrogen-vacancy centers
in a high-purity diamond sample at low temperature. When stress is applied to the sample it is possible to
observe coherent population trapping with a single center. By adjusting the stress it is possible to obtain a
situation in which all of the transitions from the three ground sublevels to a common excited state are strongly
allowed. These results show that all-optical spin manipulation is possible for this system, and we propose that
that by coupling single centers to optical microcavities, a scalable quantum network could be realized for photonic
quantum information processing.
We describe how a quantum non-demolition device based on electromagnetically-induced transparency in solidstate atom-like systems could be realized. Such a resource, requiring only weak optical nonlinearities, could potentially enable photonic quantum information processing (QIP) that is much more efficient than QIP based on linear optics alone. As an example, we show how a parity gate could be constructed. A particularly interesting physical system for constructing devices is the nitrogen-vacancy defect in diamond, but the excited-state structure for this system is unclear in the existing literature. We include some of our latest spectroscopic results that indicate that the optical transitions are generally not spin-preserving, even at zero magnetic field, which allows the realization of a Λ-type system.
Single electron transistors (SET) are devices that can be used as highly sensitive electrometers, with sensitivities approaching the quantum noise level. They can be used as measurement devices for quantum systems, including quantum computers and quantum-dot cellular automata, and as logic elements in their own right as replacements for MOSFETs. For solid-state quantum computing applications it is vital to maximize the charge sensitivity to decrease readout time and increase readout fidelity. We analyze the interactions between a SET and a double dot system. The SET sensitivity is described in terms of the current variation through the SET due to a single electron's location on the two dots. We use finite element modeling to determine the capacitive coupling between all objects in our system, which in turn allows us to determine the current in the SET based on steady-state energy minimization arguments. We base our geometries on experiments involving a twin-SET device developed as a prototype for solid-state quantum computing read-out. Our model allows us to systematically vary the device geometry in order to optimize the sensitivity of the SET.
We propose a scheme for electron spin quantum computing based on
electron spin in semiconductors. This scheme shares many similarities
with the existing Kane nuclear spin proposal. We show how quantum
computation may be carried out in this proposal, including single
qubit rotations and CNOT gate. We show how this control can
potentially lead to gate speeds 100-1000 times faster than the
existing nuclear spin proposal, and up to 106 times faster than a typical electron spin dephasing time, T2(e).
Direct single-spin detection for read-out in solid-state quantum computing architectures is a difficult problem due to the isolation of the spin qubit from its environment. Converting the problem to one of charge measurement is advantageous as we can measure the charge qubit using a single electron transistor (SET). The read-out state for the standard Si:P architecture -- a doubly occupied donor state D- -- results from spin-dependent electron tunneling between donors. Complications arise due to the low binding energy of this state, meaning existing adiabatic transfer schemes may cause ionisation of the D- state before measurement can be performed by the SET. We describe a new method for the read-out of spin qubits, using gated electric fields at resonance with the transition being measured, to resonantly transfer a single electron to the SET using small DC fields. In addition to this we propose an extension to this method where a far-infrared laser (FIR) induces the resonant transfer.
Quantum-dot Cellular Automata (QDCA) provide an interesting experimental system with which to study the interaction of a charge-based two-level system with the surrounding solid-state environment. This is particularly important given the recent interest in solid-state quantum computers using charge-qubits. We show that many of the properties of these qubits, coupling strength, tunnelling time, relaxation rate and dephasing time can be estimated using a QDCA cell like structure. Calculations are performed for the case of buried donors in silicon but the results are equally applicable to other forms of charge-qubit.
KEYWORDS: Quantum communications, Quantum computing, Control systems, Quantum information, Quantum dots, Silicon, Solid state electronics, Quantum networks, Semiconductors, Electron transport
Incoherent quantum charge tunneling forms the basis of semiconductor devices. However it is well known from atomic and optical work, that coherent tunneling can be significantly faster and in principle, coherent transfer is dissipationless, i.e. the charge being transferred does not exchange heat with the environment. Furthermore, adiabatic controls are inherently robust provided the adiabaticity criterion is satisfied. Adiabatic control methods are therefore preferable to ensure high-fidelity operation despite increased operating time. We describe recent work towards understanding charge transfer mechanisms based on adiabatic passage techniques with all-electrical controls in three-, five- and seven-dot systems based on Coherent Tunneling Adiabatic Paassage (CTAP). We derive analytical values for the important eigenstates and the adiabaticity criteria for these schemes. These analytical results allow us to make comments regarding the scalability of these schemes to realistic quantum networks.
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