We present a widefield microscopy system for imaging super-paramagnetic nanoparticles (SPNs), and propose to use it
as a bio-sensing system wherein SPNs are used as tags. Potential advantages of magnetic tags over conventional
fluorescent tags include the elimination of noise from auto-fluorescence, optical isolation of the biological system from
the measurement apparatus, and the potential for magnetic removal of non-specifically bound material. The microscope
magnetic sensing surface is composed of a thin layer of nitrogen-vacancy defect centers in the top 200 nm of a diamond
substrate. Nitrogen-vacancy centers in diamond have been shown to be suitable for use as highly sensitive
magnetometers due to their long spin-coherence time at room temperature. Furthermore, spin-dependent
photoluminescence allows for simple far-field optical readout of the spin state, which in turn allows for opticallydetected
magnetic resonance measurements. We will present our results detecting a single, lithographically defined 50
nm diameter by 100 nm thick iron nanodot. With the current sensitivity of 9 μT⋅Hz-1/2, we expect to be able to detect single 20 nm magnetite SPNs, our proposed tags, in less than one minute. By further optimizing the sensor surface, we predict DC magnetic sensitivities as low as 1 μT⋅Hz-1/2.
Nitrogen-vacancy (NV) centers coupled to scalable optical networks have the potential to realize solid-state quantum information processing platforms. Toward this goal, we demonstrate coupling of near-surface NV- centers to an array of GaP optical resonators. The use of GaP as the optical waveguiding materials is appealing due to the possibility of realizing integrated photonic switches based on the linear electro-optic effect. We explore large-area integration of GaP on diamond through two routes: molecular beam deposition directly onto diamond substrates and layer transfer of single-crystalline sheets. While the direct deposition benefits from simpler, monolithic processing, the layer transfer route benefits from higher material quality. In the latter approach, we demonstrate the transfer of submicrometer thick, mm2-sized GaP sheets from a GaP/AlGaP/GaP substrate to a diamond sample prepared with near-surface NV- centers. We fabricate large arrays of GaP disk resonators with varying diameters (1 to 20 μm) on the diamond substrate via electron beam lithography and dry etching, and show coupling of the NV- center emission to the cavity structures. Quality factors above 10,000 were observed in 5 μm diameter disks on the non-etched diamond substrate. Similar quality factors in smaller sized devices are expected with diamond substrate etching to further confine the optical mode. This approach opens a path towards the integration of coupled optical components in the hybrid GaP/diamond system, an essential step towards large-scale photonic networks utilizing NV- centers in diamond.
We demonstrate coupling between the zero phonon line (ZPL) of nitrogen-vacancy centers in diamond and the
modes of optical micro-resonators fabricated in single crystal diamond membranes sitting on a silicon dioxide
substrate. A more than ten-fold enhancement of the ZPL is estimated by measuring the modification of the
spontaneous emission lifetime. The cavity-coupled ZPL emission was further coupled into on-chip waveguides
thus demonstrating the potential to build optical quantum networks in this diamond on insulator platform.
The combination of the long electron state spin coherence time and the optical coupling of the ground electronic
states to an excited state manifold makes the nitrogen-vacancy (NV) center in diamond an attractive candidate
for quantum information processing. To date the best spin and optical properties have been found in centers
deep within the diamond crystal. For useful devices it will be necessary to engineer NVs with similar properties
close to the diamond surface. We report on properties including charge state control and preferential orientation
for near surface NVs formed either in CVD growth or through implantation and annealing.
Nitrogen-vacancy centers in diamond are widely studied both as a testbed for solid state quantum optics and for
their applications in quantum information processing and magnetometry. Here we demonstrate coupling of the
nitrogen-vacancy centers to gap plasmons in metal nano-slits. We use diamond samples where nitrogen-vacancy
centers are implanted tens of nanometers under the surface. Silver nano-slits are patterned on the sample such
that diamond ridges tens of nanometers wide fill the slit gap. We measure enhancement of the spontaneous
emission rate of the zero photon line by a factor of 3 at a temperature of 8K.
Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence
time, T2, of a spin system. We report on the experimental implementation of all-optical spin echo to determine
the T2 time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an
arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo
techniques using microwaves, ultrafast optical pulses allow clean T2 measurements of systems with dephasing
times (T *2 ) fast in comparison to the timescale for microwave control. We measure a 7 μs coherence time, which
is similar to previous measurements in quantum dots and indicates that nuclear spin diffusion is the primary
mechanism for decoherence. This demonstration is a critical step towards optical, dynamic decoupling, which
can eliminate fast decoherence and can be integrated into quantum computer architectures based on opticallycontrolled
spin qubits.
The understanding of the coherence properties of photons emitted from negatively charged nitrogen-vacancy (NV)
centers in diamond is essential for the success of quantum information applications based on indistinguishable
photons. Here we study both the polarization of photons emitted from and the linewidth of photons absorbed by
single NV centers as a function of temperature T. We find that for T < 100 K the main dephasing mechanism
contributing to the linewidth broadening is phonon-mediated population transfer between the two excited orbital
states. The observed T5 temperature dependence of the population transfer rate and linewidth is experimental
evidence of a dynamic Jahn-Teller effect in the excited states.
We describe research on new optical structures in diamond for quantum information and sensing applications
based on the nitrogen-vacancy (NV) center. Results include etching experiments that reveal the vertical distribution
of NV centers produced by ion implantation and annealing, and gallium phosphide waveguides fabricated
on diamond with evanescent coupling to NV centers close to the diamond surface.
Spatial and k-space properties of subwavelength cross-section GaP waveguides supported by a diamond substrate are
analyzed theoretically. These waveguides are suitable for optically coupling to nitrogen vacancy centers located near the
surface of a single crystal diamond sample.
We observe the coupling of nitrogen-vacancy centers in single-crystal diamond to GaP waveguides on the diamond
surface. We describe the fabrication procedure and characterize the waveguide performance. Our results
indicate that the GaP/diamond hybrid system is a promising system for coupling nitrogen-vacancies to optical
microstructures for quantum information processing and sensing applications.
Scalable quantum information processing using nitrogen-vacancy (NV) centers in diamond will be difficult without
the ability to couple the centers to optical microcavities and waveguides. Here we present our preliminary
result of coupling a single NV center in a nanoparticle to a silica microdisk at cryogenic temperatures. The
cavity-coupled NV photoluminescence is coupled out of the cavity through a tapered fiber. Although the current
system is limited by the spectral properties of the NV center and the Q of the cavity, efficient particle-cavity
and cavity-waveguide coupling should lead to the realization of a "one-dimensional atom" as needed for CQED,
enable single-shot electron-spin readout, and increase the probability of success in entanglement schemes based
on single-photon detection.
General requirements for single-photon devices in various applications are presented and compared with experimental
progress to date. The quantum information applications that currently appear the most promising require
a matter qubit-enabled single-photon source, where the emitted photon state is linked to the state of a long-lived
quantum system such as an electron spin. The nitrogen-vacancy center in diamond is a promising solid-state
system for realizing such a device due to its long-lived electron spin coherence, optical addressability, and ability
to couple to a manageable number of nuclear spins. This system is discussed in detail, and experimental results
from our laboratory are shown. A critical component of such a device is an optical microcavity to enhance the
coupling between the nitrogen-vacancy center and a single photon, and we discuss theoretically the requirements
for achieving this enhancement.
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