Constructive Quantum Interference Research Articles

The effect of two-photon quantum interference on amplitude-squared squeezing of a quantum field

In this paper, we consider a superposition of a weak coherent field and a two-photon source and examine the amplitude-squared squeezing (ASS) properties of the combined field. We demonstrate that the efficient and lasting ASS effect of the field could be observed due to constructive two-photon quantum interference. The relationship between ASS and photon antibunching effects is discussed. It is found that photon antibunching may accompany weak ASS, but in most cases ASS effects appear accompanying photon bunching.

Observations of absorptive photon switching and suppression of two-photon absorption in cold atoms

Atomic coherence and interference in an atomic medium exhibiting electromagnetically induced transparency may lead to enhancement or suppression of nonlinear susceptibilities. Absorptive photon switching has been observed by constructive quantum interference, which is based on the enhanced third-order, nonlinear absorption in a four-level system. In a different four-level system, suppression of the two-photon absorption by destructive quantum interference has been observed. Experiments were carried out on 87Rb atoms cooled and confined in a magneto-optical trap and the experimental results agree with theoretical calculations of simple four-level model systems.

Experimental Observation of Constructive Quantum Interferencevia Hybrid Excitation in an Na2-Na System

We report on an experimental observation of constructive quantum interferencebetween two atomic transition pathways 3P1/2-5S (or 4D) and3P3/2-5S (or 4D) via equal-frequency hybrid excitation andcollision-aided radiative excitation in an Na2-Na system. Through thespecial excitation processes, constructive quantum interference is realizedfor a Λ-type quantum-beat configuration with a widely-spaceddoublet (about 17 cm-1) in the excited sodium atom driven by one laser.The dependences of quantum interference on the argon buffer gas pressure andsample temperature are also examined.

Atomic four-wave mixing: fermions versus bosons.

We compare four-wave mixing in quantum degenerate gases of bosonic and fermionic atoms. We find that matter-wave gratings formed from either bosonic or fermionic atoms can in principle exhibit nearly identical Bragg scattering and four-wave mixing properties. This implies that effects such as coherent matter-wave amplification and superradiance can occur in degenerate Fermi gases. This effect is due to constructive many-particle quantum interferences, which in the boson case are interpreted as "Bose enhancement."

Nonlinear absorption by quantum interference in cold atoms

We report an experimental observation of third-order nonlinear absorption by quantum interference in (87)Rb atoms cooled and confined in a magneto-optic trap. A coupling laser creates electromagnetically induced transparency (EIT) in a multilevel Rb system in which the third-order nonlinear absorption is enhanced by constructive quantum interference while the linear absorption is inhibited by destructive interference. Our experiment demonstrates the EIT system proposed by Harris and Yamamoto [Phys. Rev. Lett. 81, 3611 (1998)], which absorbs two photons but not one photon in the dressed-state picture.

Nonlinear excitation by quantum interference in a Doppler-broadened rubidium atomic system

We analyze nonlinear excitation in a four-level atomic system that exhibits electromagnetically induced transparency induced by a strong coupling laser. We show that, at the line center of the atomic transition, the nondegenerate two-photon excitation in the dressed states can be enhanced by constructive quantum interference in two excitation paths while the linear absorption is inhibited by destructive quantum interference. We report an experimental study of the interference-enhanced two-photon absorption in a multilevel Λ-type rubidium atomic system and compare the measurements with the theoretical calculations.

Excess conductance of superconductor-semiconductor interfaces due to phase conjugation between electrons and holes.

A semiclassical description is given of charge transport through a superconductor-semiconductor interface. As a result of the presence of a potential barrier both Andreev and normal reflection occur. Elastic scatterers in the semiconductor generate multiple reflections at the interface. The constructive quantum interference which results from the phase conjugation between electrons and holes enhances the (differential) conductance above its classical value. This excess conductance is suppressed by a magnetic field, or by a finite energy. The latter can be due to a finite voltage bias or a finite temperature.