Exponential sensitivity to dephasing of electrical conduction through a quantum dot.

Area of Science:

• Quantum physics
• Condensed matter physics
• Mesoscopic systems

Background:

• Random-matrix theory predicts interference effects in ballistic chaotic quantum dots vanish with decreasing dephasing time (τφ) compared to dwell time (τD).
• Aleiner and Larkin proposed a crossover to exponential suppression when τφ drops below the Ehrenfest time (τE).

Purpose of the Study:

• To report the first observation of the crossover from power-law to exponential suppression of interference effects in quantum dot conductance.
• To validate a modified random-matrix theory for quantum dots, explaining observed phenomena in both dephasing and non-dephasing regimes.

Main Methods:

• Computer simulations of universal conductance fluctuations in ballistic chaotic quantum dots.
• Analysis of interference effects in conductance as a function of dephasing time (τφ) and dwell time (τD).

Main Results:

• Observed a crossover from power-law to exponential suppression of interference effects as τφ decreased below τE.
• Demonstrated that the modified random-matrix theory accurately explains the observed crossover and conductance fluctuations.
• Showed that the theory also explains the absence of predicted exponential suppression in the non-dephasing regime (τφ → ∞).

Conclusions:

• The crossover from power-law to exponential suppression of interference effects in quantum dot conductance is experimentally observable.
• An effective random-matrix theory successfully describes quantum dot conductance, incorporating dephasing effects and explaining previously unexplained phenomena.