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Register a new userRadiative-field quantum-coupling between closely-spaced surfaces
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Added by
Andrew Meulenberg Jr.
Publication date
2009
fields
Physics
and research's language is
English
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A quantum-mechanical formulation of energy transfer between closely-spaced surfaces is given. Coupling between the two surfaces arises from the atomic dipole-dipole interaction involving transverse-photon exchange. The exchange of photons at resonance greatly enhances the radiation transfer. The spacing (distance) dependence is derived for the quantum well - quantum well situation. The interaction between two planar quantum wells, separated by a gap is found to be proportional to the 4th power of the wavelength-to-gapwidth ratio and to the radiation tunneling factor for the evanescent waves. Expressions for the net power transfer, in the near-field regime, from hot to cold surface for this case is given and evaluated for representative materials. Computational modeling of selected, but realizable, emitter and detector structures and materials shows the benefits of both near-field and resonance coupling (e.g., with 0.1 micron gaps).
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A quantum-mechanical formulation of energy transfer between closely spaced surfaces is given. Coupling between the two surfaces arises from the atomic dipole-dipole interaction involving transverse-photon exchange. The exchange of photons at resonance enhances the radiation transfer. The interaction between two surfaces, separated by a gap, is found to be dependent upon geometric, material, frequency, dipole, and temperature factors, along with a radiation-tunneling factor for the evanescent waves. The derived geometric term has a gap-spacing (distance) dependence that varies inversely as the second power for bulk samples to the inverse fourth power for the quantum well - quantum well case. Expressions for the net power transfer, in the near-field regime, from hot to cold surface for this case is given and evaluated for representative materials.
Variations in the electrostatic surface potential between the proof mass and electrode housing in the space-based gravitational wave mission LISA is one of the largest contributors of noise at frequencies below a few mHz. Torsion balances provide an ideal testbed for investigating these effects in conditions emulative of LISA. Our apparatus consists of a Au coated Cu plate brought near a Au coated Si plate pendulum suspended from a thin W wire. We have measured a white noise level of $30, uVhz$ above approximately 0.1, mHz, rising at lower frequencies, for the surface potential variations between these two closely spaced metals.
In this paper, we present experimental techniques to resolve the closely spaced hyperfine levels of a weak transition by eliminating the residual/partial two-photon Doppler broadening and cross-over resonances in a wavelength mismatched double resonance spectroscopy. The elimination of the partial Doppler broadening is based on velocity induced population oscillation (VIPO) and velocity selective saturation (VSS) effect followed by the subtraction of the broad background of the two-photon spectrum. Since the VIPO and VSS effect are the phenomena for near zero velocity group atoms, the subtraction gives rise to Doppler-free peaks and the closely spaced hyperfine levels of the $6text{P}_{3/2}$ state in Rb are well resolved. The double resonance experiment is conducted on $5text{S}_{1/2}rightarrow5text{P}_{3/2}$ strong transition (at 780~nm) and $5text{S}_{1/2}rightarrow6text{P}_{3/2}$ weak transition (at 420~nm) at room temperature.
Electron and nuclear spins of diamond nitrogen-vacancy (NV) centers are good candidates for quantum information processing as they have long coherence time and can be initialized and read out optically. However, creating a large number of coherently coupled and individually addressable NV centers for quantum computing has been a big challenge. Here we propose methods to use high-density diamond NV centers coupled by spin-spin interaction with an average separation on the order of 10 nm for quantum computing. We propose to use a strain gradient to encode the position information of each NV center in the energy level of its excited electron orbital state, which causes a shift of its optical transition frequency. With such strain encoding, more than 100 closely-packed NV centers below optical diffraction limit can be read out individually by resonant optical excitation. A magnetic gradient will be used to shift the electron spin resonant (ESR) frequencies of NV centers. Therefore, the spin state of each NV center can be individually manipulated and different NV centers can be selectively coupled. A universal set of quantum operations for two-qubit and three-qubit system is introduced by careful design of external drives. Moreover, entangled states with multiple qubits can be created by this protocol, which is a major step towards quantum information processing with solid-state spins.
Electromagnetically induced transparency (EIT) is a well-known phenomenon due in part to its applicability to quantum devices such as quantum memories and quantum gates. EIT is commonly modeled with a three-level lambda system due to the simplicity of the calculations. However, this simplified model does not capture all the physics of EIT experiments with real atoms. We present a theoretical study of the effect of two closely-spaced excited states on EIT and off-resonance Raman transitions. We find that the coherent interaction of the fields with two excited states whose separation is smaller than their Doppler broadened linewidth can enhance the EIT transmission and broaden the width of the EIT peak. However, a shift of the two-photon resonance frequency for systems with transitions of unequal dipole strengths leads to a reduction of the maximum transparency that can be achieved when Doppler broadening is taken into account even under ideal conditions of no decoherence. As a result, complete transparency cannot be achieved in a vapor cell. Only when the separation between the two excited states is of the order of the Doppler width or larger can complete transparency be recovered. In addition, we show that off-resonance Raman absorption is enhanced and its resonance frequency is shifted. Finally, we present experimental EIT measurements on the D1 line of $^{85}$Rb that agree with the theoretical predictions when the interaction of the fields with the four levels is taken into account.
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