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Quantum optics with atom-like systems in diamond
The nitrogen vacancy (NV) center in diamond is a unique quantum system that combines solid state spin qubits with coherent optical transitions. The spin states of the NV center can be initialized, read out, and controlled with RF fields at room temperature. It can be coupled to other spin systems in the environment while at the same time maintaining an extraordinary degree of quantum coherence. Experiments utilizing the NV center's spin states have led to a wide range of demonstrations from quantum error correction to high-sensitivity magnetometry. This thesis, however, focuses on creating an interface between NV centers and light in the visible domain by making use of its optical transitions. Such an interface connects the quantum system consisting of NV centers and nuclear spins to photons, which can then be used to both manipulate the spin qubits themselves or transport quantum information over large distances.Physic
Loading rubidium atoms into a hollow core fiber
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 71-73).We demonstrate a procedure for cooling, trapping, and transferring rubidium atoms into a hollow core photonic band gap fiber. The atoms are first collected in a magneto-optical trap (MOT) and then cooled using polarization gradient cooling. Magnetic traps are then used to confine and transfer the atoms toward the face of the fiber. An optical dipole trap formed using laser light propagating through the fiber guide the atoms and confine them away from the fiber walls. We hope to use this system to achieve large optical depths with possible applications to quantum computing.by Yiwen Chu.S.B
Unrevealing hardening and strengthening mechanisms in high-entropy ceramics from lattice distortion
Revealing the hardening and strengthening mechanisms is crucial for
facilitating the design of superhard and high-strength high-entropy ceramics
(HECs). Here, we take high-entropy diborides (HEB) as the prototype to
thoroughly investigate the hardening and strengthening mechanisms of HECs.
Specifically, the equiatomic 4- to 9-cation single-phase HEB ceramics
(4-9HEB) are fabricated by an ultra-fast high-temperature sintering method.
The as-fabricated 4-9HEB samples possess similar grain sizes, comparable
relative densities (up to ~98%), uniform compositions, and clean grain
boundaries without any impurities. The experimental results show that the
hardness and flexural strength of the as-fabricated 4-9HEB samples have an
increasing tendency with the increase of metal components. The first-principles
calculations find that lattice distortion is essential to the hardness and
strength of HEB. With the increase of metal components, an aggravation of
lattice distortion accompanied by B-B bond strengthening is determined,
resulting in the enhancement of the hardness and flexural strength. Moreover,
the correlation between other potential indicators and the hardness/flexural
strength of HEB has been disproved, including valence electron
concentration, electronegativity mismatch, and metallic states. Our results
unravel the hardening and strengthening mechanisms of HECs by intensifying
lattice distortion, which may provide guidance for developing superhard and
high-strength HECs
Schr\"odinger cat states of a 16-microgram mechanical oscillator
The superposition principle is one of the most fundamental principles of
quantum mechanics. According to the Schr\"odinger equation, a physical system
can be in any linear combination of its possible states. While the validity of
this principle is routinely validated for microscopic systems, it is still
unclear why we do not observe macroscopic objects to be in superpositions of
states that can be distinguished by some classical property. Here we
demonstrate the preparation of a mechanical resonator with an effective mass of
16.2 micrograms in Schr\"odinger cat states of motion, where the constituent
atoms are in a superposition of oscillating with two opposite phases. We show
control over the size and phase of the superposition and investigate the
decoherence dynamics of these states. Apart from shedding light at the boundary
between the quantum and the classical world, our results are of interest for
quantum technologies, as they pave the way towards continuous-variable quantum
information processing and quantum metrology with mechanical resonators
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