4,028 research outputs found
Lean Principles:: Can Proven Manufacturing Techniques Benefit an Information Technology Organization?
The benefits of Lean Principles have been reaped in manufacturing for many years and have been seen recently in other verticals. A comprehensive review of the scientific literature exposed that within the information technology field, Lean Principles remains relatively unknown or used. As corporate senior management seek to save costs, information technology needs to provide clear and concise guidance on how to maximize production efficiencies while minimizing costs. If a company cannot leverage information technology properly, staffing and budget cuts are likely. This paper discusses the potential benefits for information technology organizations to utilize Lean Principles. A case study revealed that in a short period of time an information technology group within an education institution implemented information technology improvements that actualized some of the benefits of Lean Principles
Fast spin rotations by optically controlled geometric phases in a quantum dot
We demonstrate optical control of the geometric phase acquired by one of the
spin states of an electron confined in a charge-tunable InAs quantum dot via
cyclic 2pi excitations of an optical transition in the dot. In the presence of
a constant in-plane magnetic field, these optically induced geometric phases
result in the effective rotation of the spin about the magnetic field axis and
manifest as phase shifts in the spin quantum beat signal generated by two
time-delayed circularly polarized optical pulses. The geometric phases
generated in this manner more generally perform the role of a spin phase gate,
proving potentially useful for quantum information applications.Comment: 4 pages, 3 figures, resubmitted to Physical Review Letter
All-Optical Ultrafast Control and Read-Out of a Single Negatively Charged Self-Assembled InAs Quantum Dot
We demonstrate the all-optical ultrafast manipulation and read-out of optical
transitions in a single negatively charged self-assembled InAs quantum dot, an
important step towards ultrafast control of the resident spin. Experiments
performed at zero magnetic field show the excitation and decay of the trion
(negatively charged exciton) as well as Rabi oscillations between the electron
and trion states. Application of a DC magnetic field perpendicular to the
growth axis of the dot enables observation of a complex quantum beat structure
produced by independent precession of the ground state electron and the excited
state heavy hole spins
The effect of photo-generated carriers on the spectral diffusion of a quantum dot coupled to a photonic crystal cavity
We experimentally observe the effect of photo-generated carriers on the
spectral diffusion of a quantum dot (QD) coupled to a photonic crystal (PC)
cavity. In this system, spectral diffusion arises in part from charge
fluctuations on the etched surfaces of the PC. We find that these fluctuations
may be suppressed by photo-generated carriers, leading to a reduction of the
measured QD linewidth by a factor of ~2 compared to the case where the
photo-generated carriers are not present. This result demonstrates a possible
means of countering the effects of spectral diffusion in QD-PC cavity systems
and thus may be useful for quantum information applications where narrow QD
linewidths are desired
Covering Points by Disjoint Boxes with Outliers
For a set of n points in the plane, we consider the axis--aligned (p,k)-Box
Covering problem: Find p axis-aligned, pairwise-disjoint boxes that together
contain n-k points. In this paper, we consider the boxes to be either squares
or rectangles, and we want to minimize the area of the largest box. For general
p we show that the problem is NP-hard for both squares and rectangles. For a
small, fixed number p, we give algorithms that find the solution in the
following running times:
For squares we have O(n+k log k) time for p=1, and O(n log n+k^p log^p k time
for p = 2,3. For rectangles we get O(n + k^3) for p = 1 and O(n log n+k^{2+p}
log^{p-1} k) time for p = 2,3.
In all cases, our algorithms use O(n) space.Comment: updated version: - changed problem from 'cover exactly n-k points' to
'cover at least n-k points' to avoid having non-feasible solutions. Results
are unchanged. - added Proof to Lemma 11, clarified some sections - corrected
typos and small errors - updated affiliations of two author
The Coherent Optical Spectroscopy and Control of an Electron Spin in a Self-Assembled Quantum Dot for Quantum Computing.
Self-assembled quantum dots (QDs) containing a single electron are one of the leading candidate systems for the realization of a quantum computer. The spin states of charges confined in these dots have been shown to possess a number of qualities that are attractive for use as the quantum bits (qubits) in quantum computing implementations, particularly their long lifetimes and coherence times. In addition, these spin qubits may be controlled optically, offering the prospect of ultrafast qubit gate operations, a crucial necessity for the execution of quantum algorithms. Due to the weak interaction of self-assembled QDs with light, however, the coherent optical control and read-out of the spin states of charged self-assembled QDs has proven to be a considerable challenge.
This thesis presents two sets of experiments demonstrating the coherent optical control and read-out of the quantum states of a self-assembled InAs QD containing a single electron. The first utilizes mode-locked picosecond optical pulses to control the optical transitions in the dot and to detect QD level occupations. These capabilities are used to observe transient phenomena in a singly charged InAs QD such as the generation and decay of excited state population and spin precession. Further, Rabi oscillations between the electron and the lowest-lying excited state are observed, demonstrating the ability to coherently control the optical transitions of the QD, a prerequisite for spin control.
These results are built upon in the second set of experiments, in which a combination of optical pulses, an externally applied DC magnetic field and a continuous-wave (CW) optical field are employed to initialize and completely control the states of a QD confined electron spin. Spin control by the use of pulse-driven two-photon Raman processes, spin precession about the external magnetic field and geometric phases generated by CW-driven cyclic evolutions in the dot is demonstrated. A number of spin qubit gate operations are shown for these spin control mechanisms, forming a foundational set of single qubit gates required for the implementation of quantum computing with singly charged self-assembled QDs.Ph.D.Applied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64774/1/erikdkim_1.pd
Bichromatic Driving of a Solid State Cavity QED System
The bichromatic driving of a solid state cavity quantum electrodynamics
system is used to probe cavity dressed state transitions and observe coherent
interaction between the system and the light field. We theoretically
demonstrate the higher order cavity-dressed states, supersplitting, and AC
stark shift in a solid state system comprised of a quantum dot strongly coupled
to a photonic crystal cavity for on- and far off-resonant cases. For the
off-resonant case, phonons mediate off-resonant coupling between the quantum
dot and the photonic resonator, a phenomenon unique to solid state cavity
quantum electrodynamics.Comment: 8 pages 6 figure
Proposed Coupling of an Electron Spin in a Semiconductor Quantum Dot to a Nanosize Optical Cavity
We propose a scheme to efficiently couple a single quantum dot electron spin
to an optical nano-cavity, which enables us to simultaneously benefit from a
cavity as an efficient photonic interface, as well as to perform high fidelity
(nearly 100%) spin initialization and manipulation achievable in bulk
semiconductors. Moreover, the presence of the cavity speeds up the spin
initialization process beyond GHz.Comment: 6 figure
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