We demonstrate a complete set of fast, all-optical single-qubit operations on a single electron spin confined in a
semiconductor quantum dot (QD). Optical initialization and measurement of the single spin are accomplished by optical
pumping in a 3.4 ns timescale with 92±7% fidelity. The spin is coherently manipulated by a single red-detuned
broadband laser pulse with 4 picosecond duration. We achieve over six complete Rabi oscillations between the two spin
states by varying the rotation pulse's intensity. The fidelity of π/2 and π rotations both exceed 90%. Next we use two
sequential rotation pulses, separated by a variable time delay, to demonstrate a complete set of Ramsey fringes. This
two-pulse sequence is sufficient to achieve an arbitrary rotation of the spin and thus serves as a universal single-qubit
In systems with sizable spin-orbit interaction intense optical illumination or an electric field can generate an
effective "pseudomagnetic field" which replaces a true applied magnetic field for the efficient and rapid manipulation
of spins. The theoretical characteristics of optically-induced spin precession in self-assembled quantum
dots will be described, along with the potential for manipulating spins bound to donors and acceptors with
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.
The ability to sense nanotelsa magnetic fields with nanoscale spatial resolution is an outstanding technical
challenge relevant to the physical and biological sciences. For example, detection of such weak localized fields
will enable sensing of magnetic resonance signals from individual electron or nuclear spins in complex biological
molecules and the readout of classical or quantum bits of information encoded in an electron or nuclear spin
memory. Here we present a novel approach to nanoscale magnetic sensing based on coherent control of an
individual electronic spin contained in the Nitrogen-Vacancy (NV) center in diamond. At room temperature,
using an ultra-pure diamond sample, we achieve shot-noise-limited detection of 3 nanotesla magnetic fields
oscillating at kHz frequencies after 100 seconds of signal averaging. Furthermore, we experimentally demonstrate
nanoscale resolution using a diamond nanocrystal of 30 nm diameter for which we achieve a sensitivity of 0.5
microtesla / Hz1/2.
The strong coupling regime between a single emitter and the mode of an optical resonator allows for nonlinear
optics phenomena at extremely low light intensities. Down to the single photon level, extreme nonlinearities can
be observed, where the presence of a single photon inside the resonator either blocks or enhances the probability
of subsequent photons entering the resonator. In this paper we experimentally show the existence of these
phenomena, named photon blockade and photon induced tunneling, in a solid state system composed of a
photonic crystal cavity with a strongly coupled quantum dot.
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.
We coherently probe a quantum dot that is strongly coupled to a photonic crystal nano-cavity by scattering of a resonant laser beam.
The coupled system's response is highly nonlinear as the quantum dot saturates with nearly one photon per cavity lifetime. This system
enables large amplitude and phase shifts of a signal beam via a control beam, both at single photon levels. We demonstrate photon-photon
interactions with short pulses in a system that is promising for ultra-low power switches and two-qubit quantum gates.
Proc. SPIE 7225, Photorefractive time-domain differential detection method for high-precision distinction of phase-modulated signals in holographic data storage, 72250G (3 February 2009); doi: 10.1117/12.807795
We develop a photorefractive time-domain differential detection (PR-TDDD) method in holographic data storage
systems with considering the temporal response of photorefractive two-wave mixing (PR-TWM). Optimizing the
parameters of PR-TDDD method provides high-precision distinction of phase-modulated signals, i.e. distinction of small
phase difference. In PR-TDDD method, the phase information can be sequentially-distinguished by monitoring the
output intensity of PR-TWM. This is because the output intensity of PR-TWM is changed when the signal phase is
changed. In addition, the changing rate of the output intensity corresponds to that of the signal phase. The advantages of
our method are high energy efficiency, alignment-free optics and the distinction of multi-valued phase-modulated signals.
Especially, we focus attention on applying to phase-based holographic data storage systems, which can achieve
homogeneous intensity distribution on recording plane, i.e. Fourier transform plane, in general, and high energy
efficiency because of 100% white rate. More noteworthy is that multi-valued phase-based holographic data storage can
be realized by using PR-TDDD method. In this work, we consider the important parameters in PR-TDDD method;
signal-to-pump beam intensity ratio, photorefractive coupling strength, and photorefractive time constant. The balance
between these parameters is important for realizing the high-precision distinction of phase-modulated signal.
Many schemes for optical quantum computation and long-distance quantum communication require quantum
interference between indistinguishable single-photon states generated from large numbers of independent sources. Solidstate
systems allow integration of such sources on a chip. It is therefore desirable to achieve multiple solid-state singlephoton
sources for practical applications. We show a promising candidate for this in the single photons generated by the
radiative decay processes of excitons that are bound to isolated fluorine donor impurities in ZnSe/ZnMgSe quantum well
nanostructures. Donor-bound-exciton single-photon sources typically have a narrow distribution of center wavelengths,
and they overcome dipole dephasing due to their fast radiative decay time. The emitter we introduce here demonstrates
these advantages, showing strong potential for allowing quantum interference between single photons emitted by
independent solid-state single-photon sources.
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.
Radiation pressure exerted by light in interferometric measurements is responsible for displacements of mirrors
which appear as an additional back-action noise and limit the sensitivity of the measurement. We experimentally
study these effects by monitoring in a very high-finesse optical cavity the displacements of a mirror with a
sensitivity at the 10-20m/√Hz level. This unique sensitivity is a step towards the first observation of the
fundamental quantum effects of radiation pressure and the resulting standard quantum limit in interferometric
measurements. Our experiment may become a powerful facility to test quantum noise reduction schemes, and
we already have demonstrated radiation-pressure induced correlations between two optical beams sent into the
same moving mirror cavity. Our scheme can be extended down to the quantum level and has applications both
in high-sensitivity measurements and in quantum optics.
We present a model for quantum Mie scattering in one dimension, and show that quantum states of light, such as
Fock states, exhibit the same transmission functions as coherent states for an ordinary intensity measurement. If
a number-resolving measurement is carried out instead, we observe narrower transmission functions than for the
classical case. We discuss applications of this effect for high-precision length measurements in interferometry.
We present a study of dynamical decoupling schemes for the suppression of phase errors from various noise
environments using ions in a Penning trap as a model ensemble of qubits. By injecting frequency noise we
demonstrate that in an ohmic noise spectrum with a sharp, high-frequency cutoff the recently proposed UDD
decoupling sequence gives noise suppression superior to the traditional CPMG technique. Under only the influence
of ambient magnetic field fluctuations with a 1/ω4 power spectrum, we find little benefit from using the
UDD sequence, consistent with theoretical predictions for dynamical decoupling performance in the presence of
noise spectra with soft cutoffs. Finally, we implement an optimization algorithm using measurement feedback,
demonstrating that local optimization of dynamical decoupling can further lead to significant gains in error
suppression over known sequences.
It has been known for a while that, provided by the Heisenberg Uncertainty Principle, certain types of quantum
correlated light should yield a better scaling law than the one with ordinary laser light. Hitherto, however,
there is no such device practically used outside laboratories. The fact that quantum correlations are easy to
be destroyed under decoherence essentially makes their utilities problematic for real world applications. For the
optical interferometers, the most significant decoherence phenomenon is the photon loss. And yet, there has been
no real-world device for quantum-enhanced sensing that overcomes the photon loss effects. In order to analyze
the photon loss effects the description of the quantum states of light calls for a density matrix formalism, rather
than the usual pure state approach. Here we take an example of the input states for the Heisenberg-limited
interferometry, namely the optimal state, and show the description of the quantum state of light based on the
reduced density matrix.