CMSP Seminar @ICTP Wednesday 2 November at 4:00 p.m. - L.Stasi Seminar Room - K. MODI

[Condensed Matter Section]

Condensed Matter & Statistical Physics Seminar
==============================

Wednesday 2 November at 4 p.m.
Luigi Stasi Seminar Room, first floor, ICTP Leonardo Building

Kavan MODI
Dept. of Physics, Monash University,Clayton, Melbourne, Australia

"Full and Efficient Characterization of Non-Markovian Quantum Processes"

Abstract:
In science, we often want to characterise the processes undergone by a 
system
of interest; this allows us to both identify the underlying physics 
driving the process
and to predict what will happen to the system the next time the process 
occurs. If
the state of the system at any time depends only on the state of the 
system at the
previous time-step and some predetermined rule then these dynamics are 
characterised
with relative ease. For instance, the dynamics of quantum mechanical 
systems in
isolation is described in this way. But, when a quantum system 
repeatedly interact
with an environment, the environment often "remembers" information about 
the
system's past. This leads to non-Markovian processes, which depend 
nontrivially
on the state of the system at all times during its evolution and they 
are not, in general,
be easily characterised using conventional techniques. Since the early 
days of quantum
mechanics it has been a challenge to describe non-Markovian processes. 
Here we will
show that using operational tools from quantum information theory we can 
fully
characterise any non-Markovian process. In general the full 
characterisation is not
efficient, as it requires exponentially large number of experiments. To 
overcome this
obstacle we map the full process to a many-body state. We show that this 
can be
achieved by using linear, in the number of time steps, amount of 
bipartite entanglement.
Next, the state can be measured to any desired precision, thus the 
process can be
characterised to any desired precision. Finally, we define a natural 
measure for the degree
of non-Markovianity.