Let me add that the scheduling conflict consists of a talk at 10:30am
that many of you may be interested in.
Title: Beyond Post-Quantum Cryptography
Speaker: Mark Zhandry, Stanford University
Date: Friday, April 5 2013
Time: 10:30AM to 12:00PM
Location: 32-G449 (PATIL/KIVA)
http://toc.csail.mit.edu/?q=node/175
Abstract: Post-quantum cryptography attempts to build classical
cryptosystems that are secure, even against a quantum adversary. The
security definitions are left mostly unchanged from the classical
setting, keeping the adversary’s interaction with the cryptosystem
classical. This models a world where the adversary has a quantum
computer, but the honest parties remain classical.
In this talk, we look beyond post-quantum cryptography to a world
where all parties have a quantum computer. Now an adversary may
interact with the honest parties in a quantum way, necessitating new
security definitions that model these interactions. We demonstrate how
to construct pseudorandom functions, message authentication codes,
signatures, and encryption schemes in the setting where the adversary
can issue quantum queries to the parties involved. We develop new
security definitions for these settings and new proof techniques for
arguing the security of our schemes.
*Joint work with Dan Boneh.
On Wed, Apr 3, 2013 at 10:54 AM, Edward Farhi <farhi(a)mit.edu> wrote:
Hi Quanta
We are going to meet this week at 2:00 because of a scheduling conflict. We will
meet in 6-310 as usual.
Best,
Eddie
Please note that on Wednesday April 24 at 4:00 in 26-214 there will be a talk by
Pierre Rouchon on quantum control.
Title: Measurement-based feedback versus coherent feedback (reservoir
engineering) for the LKB photon-box
For quantum systems exist two kinds of stabilizing feedback: measurement-based feedback
and coherent feedback relying on reservoir engineering.
In this talk, we present these two kinds of feedback for the photon-box developed by
Serge Haroche and his collaborators [0]. For the measurement-based feedback, we describe
the first experimental implementation of a full-state feedback that stabilizes
photon-number states [1,2]. The dynamics are governed by a non-linear controlled
Markov chain with the density matrix as the hidden state. The control scheme admits an
observer/controller structure. The observer provides a real-time estimation of the density
matrix. It relies on a discrete-time implementation of quantum filtering techniques and
takes into account known measurement imperfections. The controller is a stabilizing
state-feedback law based on a Lyapunov function. This function is derived from open-loop
martingales attached to the quantum non-demolition process that measures photons without
destroying them. For the coherent feedback scheme we present a recent proposal [3,4]
based on reservoir eng!
ineering to stabilize phase-cat states: it relies on a composite interaction
(dispersive/resonant/dispersive) between the photons and the probe atoms. The resulting
Kraus map describing the ensemble average of the photon dynamics admits a unique
globally stable steady-state. This steady-state is close to a phase-cat state. It is
also robust to parametric errors and decoherence.
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Edward Farhi
Cecil and Ida Green Professor of Physics
Director
Center for Theoretical Physics
Massachusetts Institute of Technology
6-300
Cambridge MA 02139
617 253 4871
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