laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

Séminaire, 17 mars 2014

Alessandro Romito (Freie Universität, Berlin, Germany)
Weak measurement of cotunneling time

Quantum mechanics allows for the existence of virtual states that have no classical analogue. While they are forbidden by energy conservation in classical mechanics, their presence within quantum mechanics as short-lived states is allowed by the time-energy uncertainty principle. Virtual state, being volatile, defy direct observation through strong measurement that would collapse the states itself.
In this talk I will discuss how a virtual state of an interacting many-body system can be detected via weak measurements. Specifically I will discuss a weak value (WV) protocol, consisting of a weak measurement followed by a strong measurement for the determination of the time it takes an electron to tunnel through a virtual state of a quantum dot (QD). Such a cotunneling process is strikingly different from a single particle tunneling under the barrier, since here transport of an electron involves a virtual many-body correlated state on the QD.
The analysis will focus on a realistic system-detector setup, which employs a quantum point contact (QPC) as charge detector, and I will show how the correlation function of the system-detector currents is related to the cotunneling traversal time. I will show that, contrary to classical intuition, the cotunneling time is independent of the strength of the dot-lead coupling, and the expectations based on either the uncertainty principle, or on analogy with a single particle tunneling are unfounded. In fact the cotunneling time depends parametrically on whether the cotunneling is dominated by elastic or inelastic processes.