649 research outputs found
One-Sided Device-Independent Certification of Unbounded Random Numbers
The intrinsic non-locality of correlations in Quantum Mechanics allow us to
certify the behaviour of a quantum mechanism in a device independent way. In
particular, we present a new protocol that allows an unbounded amount of
randomness to be certified as being legitimately the consequence of a
measurement on a quantum state. By using a sequence of non-projective
measurements on single state, we show a more robust method to certify unbounded
randomness than the protocol of Churchod et al., by moving to a one-sided
device independent scenario. This protocol also does not assume any specific
behaviour of the adversary trying to fool the participants in the protocol,
which is an advantage over previous steering based protocols. We present
numerical results which confirm the optimal functioning of this protocol in the
ideal case. Furthermore, we also study an experimental scenario to determine
the feasibility of the protocol in a realistic implementation. The effect of
depolarizing noise is examined, by studying a potential state produced by a
networked system of ion traps.Comment: In Proceedings PC 2018, arXiv:1807.1056
Maximal randomness expansion from steering inequality violations using qudits
We consider the generation of randomness based upon the observed violation of
an Einstein-Podolsky-Rosen (EPR) steering inequality, known as one-sided
device-independent randomness expansion. We show that in the simplest scenario
-- involving only two parties applying two measurements with outcomes each
-- that there exist EPR steering inequalities whose maximal violation certifies
the maximal amount of randomness, equal to log(d) bits. We further show that
all pure partially entangled full-Schmidt-rank states in all dimensions can
achieve maximal violation of these inequalities, and thus lead to maximal
randomness expansion in the one-sided device-independent setting. More
generally, the amount of randomness that can be certified is given by a
semidefinite program, which we use to study the behaviour for non-maximal
violations of the inequalities.Comment: 6 pages, 1 figur
Certified randomness in quantum physics
The concept of randomness plays an important role in many disciplines. On one
hand, the question of whether random processes exist is fundamental for our
understanding of nature. On the other hand, randomness is a resource for
cryptography, algorithms and simulations. Standard methods for generating
randomness rely on assumptions on the devices that are difficult to meet in
practice. However, quantum technologies allow for new methods for generating
certified randomness. These methods are known as device-independent because do
not rely on any modeling of the devices. Here we review the efforts and
challenges to design device-independent randomness generators.Comment: 18 pages, 3 figure
Certified Randomness From Steering Using Sequential Measurements
The generation of certifiable randomness is one of the most promising applications of quantum technologies. Furthermore, the intrinsic non-locality of quantum correlations allow us to certify randomness in a device-independent way, ie, we do not need to make assumptions about the devices used. Due to the work of Curchod et al. a single entangled two-qubit pure state can be used to produce arbitrary amounts of certified randomness. However, the obtaining of this randomness is experimentally challenging as it requires a large number of measurements, both projective and general. Motivated by these difficulties in the device-independent setting, we instead consider the scenario of one-sided device independence where certain devices are trusted, and others are not; a scenario motivated by asymmetric experimental set-ups such as ion-photon networks. We show how certain aspects of previous works can be adapted to this scenario and provide theoretical bounds on the amount of randomness that can be certified. Furthermore, we give a protocol for unbounded randomness certification in this scenario, and provide numerical results demonstrating the protocol in the ideal case. Finally, we numerically test the possibility of implementing this scheme on near-term quantum technologies, by considering the performance of the protocol on several physical platforms
Certification of randomness without seed randomness
The security of any cryptographic scheme relies on access to random number
generators. Device-independently certified random number generators provide
maximum security as one can discard the presence of an intruder by considering
only the statistics generated by these devices. Any of the known
device-independent schemes to certify randomness require an initial feed of
randomness into the devices, which can be called seed randomness. In this work,
we propose a one-sided device-independent scheme to certify two bits of
randomness without the initial seed randomness. For our purpose, we utilise the
framework of quantum networks with no inputs and two independent sources shared
among two parties with one of them being trusted. Along with it, we also
certify the maximally entangled state and the Bell basis measurement with the
untrusted party which is then used to certify the randomness generated from the
untrusted device.Comment: 7 pages, 1 Figur
Quantum steering: a review with focus on semidefinite programming
Quantum steering refers to the non-classical correlations that can be
observed between the outcomes of measurements applied on half of an entangled
state and the resulting post-measured states that are left with the other
party. From an operational point of view, a steering test can be seen as an
entanglement test where one of the parties performs uncharacterised
measurements. Thus, quantum steering is a form of quantum inseparability that
lies in between the well-known notions of Bell nonlocality and entanglement.
Moreover, quantum steering is also related to several asymmetric quantum
information protocols where some of the parties are considered untrusted.
Because of these facts, quantum steering has received a lot of attention both
theoretically and experimentally. The main goal of this review is to give an
overview of how to characterise quantum steering through semidefinite
programming. This characterisation provides efficient numerical methods to
address a number of problems, including steering detection, quantification, and
applications. We also give a brief overview of some important results that are
not directly related to semidefinite programming. Finally, we make available a
collection of semidefinite programming codes that can be used to study the
topics discussed in this articleComment: v2: 31 pages, 2 figures. Published version. New material added.
Matlab codes to accompany this review can be found at https://git.io/vax9
Noise-robust preparation contextuality shared between any number of observers via unsharp measurements
Multiple observers who independently harvest nonclassical correlations from a
single physical system share the system's ability to enable quantum
correlations. We show that any number of independent observers can share the
preparation contextual outcome statistics enabled by state ensembles in quantum
theory. Furthermore, we show that even in the presence of any amount of white
noise, there exists quantum ensembles that enable such shared preparation
contextuality. The findings are experimentally realised by applying sequential
unsharp measurements to an optical qubit ensemble which reveals three shared
demonstrations of preparation contextuality.Comment: H. A. and N. W. contributed equally to this wor
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