The effect of frequency-mismatched spontaneous emission on atom-field entanglement

A Schrödinger representation approach is used to calculate the atom-field dynamics following spontaneous emission by an atom in its excited state to a superposition of its two ground-state sublevels, in the case where the frequency separation of the ground-state sublevels is large compared to the excited-state decay rate. The emitted radiation is incident on a broadband photodetector. Using a relatively simple model for the photodetector, we show how a measurement of a photo-signal leaves the atom in a coherent superposition of the two ground states. The relative phase between the two ground-state amplitudes can be interpreted in terms of the temporal phase acquired in the time interval between spontaneous emission (viewed as a quantum jump process) and detection. Alternatively, the phase can be associated with a spatial phase of the entangled atom-field system; the source atom is projected into a state containing this spatial phase when the emitted photon is detected.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98599/1/0953-4075_45_12_124020.pd

Non-Hermitian dispersion sign reversal of radiative resonances in two dimensions

In a recent publication [Wurdack et al., Nat. Comm. 14:1026 (2023)], it was shown that in microcavities containing atomically thin semiconductors non-Hermitian quantum mechanics can lead to negative exciton polariton masses. We show that mass-sign reversal can occur generally in radiative resonances in two dimensions (without cavity) and derive conditions for it (critical dephasing threshold etc.). In monolayer transition-metal dichalcogenides, this phenomenon is not invalidated by the strong electron-hole exchange interaction, which is known to make the exciton massless

Single exciton trapping in an electrostatically defined 2D semiconductor quantum dot

Interlayer excitons (IXs) in 2D semiconductors have long lifetimes and spin-valley coupled physics, with a long-standing goal of single exciton trapping for valleytronic applications. In this work, we use a nano-patterned graphene gate to create an electrostatic IX trap. We measure a unique power-dependent blue-shift of IX energy, where narrow linewidth emission exhibits discrete energy jumps. We attribute these jumps to quantized increases of the number occupancy of IXs within the trap and compare to a theoretical model to assign the lowest energy emission line to single IX recombination

2D Semiconductor Nonlinear Plasmonic Modulators

A plasmonic modulator is a device that controls the amplitude or phase of propagating plasmons. In a pure plasmonic modulator, the presence or absence of a pump plasmonic wave controls the amplitude of a probe plasmonic wave through a channel. This control has to be mediated by an interaction between disparate plasmonic waves, typically requiring the integration of a nonlinear material. In this work, we demonstrate the first 2D semiconductor nonlinear plasmonic modulator based on a WSe2 monolayer integrated on top of a lithographically defined metallic waveguide. We utilize the strong coupling between the surface plasmon polaritons, SPPs, and excitons in the WSe2 to give a 73 percent change in transmission through the device. We demonstrate control of the propagating SPPs using both optical and SPP pumps, realizing the first demonstration of a 2D semiconductor nonlinear plasmonic modulator, with a modulation depth of 4.1 percent, and an ultralow switching energy estimated to be 40 aJ

Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl

Heusler alloys based magnetic tunnel junctions can potentially provide high magnetoresistance, small damping and fast switching. Here junctions with Co2FeAl as a ferromagnetic electrode are fabricated by room temperature sputtering on Si/SiO2 substrates. The doping of Boron in Co2FeAl is found to have a large positive impact on the structural, magnetic and transport properties of the junctions, with a reduced interfacial roughness and substantial improved tunneling magnetoresistance. A two-level magnetoresistance is also observed in samples annealed at low temperature, which is believed to be related to the memristive effect of the tunnel barrier with impurities.Comment: 9 pages, 4 figure

Towards Quantum Repeaters with Solid-State Qubits: Spin-Photon Entanglement Generation using Self-Assembled Quantum Dots

In this chapter we review the use of spins in optically-active InAs quantum dots as the key physical building block for constructing a quantum repeater, with a particular focus on recent results demonstrating entanglement between a quantum memory (electron spin qubit) and a flying qubit (polarization- or frequency-encoded photonic qubit). This is a first step towards demonstrating entanglement between distant quantum memories (realized with quantum dots), which in turn is a milestone in the roadmap for building a functional quantum repeater. We also place this experimental work in context by providing an overview of quantum repeaters, their potential uses, and the challenges in implementing them.Comment: 51 pages. Expanded version of a chapter to appear in "Engineering the Atom-Photon Interaction" (Springer-Verlag, 2015; eds. A. Predojevic and M. W. Mitchell