10 research outputs found
Rigidity for Monogamy-Of-Entanglement Games
In a monogamy-of-entanglement (MoE) game, two players who do not communicate
try to simultaneously guess a referee's measurement outcome on a shared quantum
state they prepared. We study the prototypical example of a game where the
referee measures in either the computational or Hadamard basis and informs the
players of her choice.
We show that this game satisfies a rigidity property similar to what is known
for some nonlocal games. That is, in order to win optimally, the players'
strategy must be of a specific form, namely a convex combination of four
unentangled optimal strategies generated by the Breidbart state. We extend this
to show that strategies that win near-optimally must also be near an optimal
state of this form. We also show rigidity for multiple copies of the game
played in parallel.
As an application, we construct for the first time a weak string erasure
scheme where the security does not rely on limitations on the parties'
hardware. Instead, we add a prover, which enables security via the rigidity of
this MoE game. Furthermore, we show that this can be used to achieve bit
commitment in a model where it is impossible classically.Comment: 46 pages, 3 figure
Quantum cryptography: key distribution and beyond
Uniquely among the sciences, quantum cryptography has driven both
foundational research as well as practical real-life applications. We review
the progress of quantum cryptography in the last decade, covering quantum key
distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK
Quantum Cryptography: Key Distribution and Beyond
Uniquely among the sciences, quantum cryptography has driven both foundational research as well as practical real-life applications. We review the progress of quantum cryptography in the last decade, covering quantum key distribution and other applications.Quanta 2017; 6: 1–47
Relativistic quantum cryptography
In this thesis we explore the benefits of relativistic constraints for
cryptography. We first revisit non-communicating models and its applications in
the context of interactive proofs and cryptography. We propose bit commitment
protocols whose security hinges on communication constraints and investigate
its limitations. We explain how some non-communicating models can be justified
by special relativity and study the limitations of such models. In particular,
we present a framework for analysing security of multiround relativistic
protocols. The second part of the thesis is dedicated to analysing specific
protocols. We start by considering a recently proposed two-round quantum bit
commitment protocol. We propose a fault-tolerant variant of the protocol,
present a complete security analysis and report on an experimental
implementation performed in collaboration with an experimental group at the
University of Geneva. We also propose a new, multiround classical bit
commitment protocol and prove its security against classical adversaries. This
demonstrates that in the classical world an arbitrarily long commitment can be
achieved even if the agents are restricted to occupy a finite region of space.
Moreover, the protocol is easy to implement and we report on an experiment
performed in collaboration with the Geneva group.Comment: 123 pages, 9 figures, many protocols, a couple of theorems, certainly
not enough commas. PhD thesis supervised by Stephanie Wehner at Centre for
Quantum Technologies, Singapor
LIPIcs, Volume 251, ITCS 2023, Complete Volume
LIPIcs, Volume 251, ITCS 2023, Complete Volum
Device-independent quantum key distribution
In this thesis, we study two approaches to achieve device-independent quantum
key distribution: in the first approach, the adversary can distribute any
system to the honest parties that cannot be used to communicate between the
three of them, i.e., it must be non-signalling. In the second approach, we
limit the adversary to strategies which can be implemented using quantum
physics. For both approaches, we show how device-independent quantum key
distribution can be achieved when imposing an additional condition. In the
non-signalling case this additional requirement is that communication is
impossible between all pairwise subsystems of the honest parties, while, in the
quantum case, we demand that measurements on different subsystems must commute.
We give a generic security proof for device-independent quantum key
distribution in these cases and apply it to an existing quantum key
distribution protocol, thus proving its security even in this setting. We also
show that, without any additional such restriction there always exists a
successful joint attack by a non-signalling adversary.Comment: PhD Thesis, ETH Zurich, August 2010. 188 pages, a