3,795 research outputs found
Quantum computational tensor network on string-net condensate
The string-net condensate is a new class of materials which exhibits the
quantum topological order. In order to answer the important question, "how
useful is the string-net condensate in quantum information processing?", we
consider the most basic example of the string-net condensate, namely the
gauge string-net condensate on the two-dimensional hexagonal lattice, and show
that the universal measurement-based quantum computation (in the sense of the
quantum computational webs) is possible on it by using the framework of the
quantum computational tensor network. This result implies that even the most
basic example of the string-net condensate is equipped with the correlation
space that has the capacity for the universal quantum computation.Comment: 5 pages, 4 figure
Continuous-variable blind quantum computation
Blind quantum computation is a secure delegated quantum computing protocol
where Alice who does not have sufficient quantum technology at her disposal
delegates her computation to Bob who has a fully-fledged quantum computer in
such a way that Bob cannot learn anything about Alice's input, output, and
algorithm. Protocols of blind quantum computation have been proposed for
several qubit measurement-based computation models, such as the graph state
model, the Affleck-Kennedy-Lieb-Tasaki model, and the
Raussendorf-Harrington-Goyal topological model. Here, we consider blind quantum
computation for the continuous-variable measurement-based model. We show that
blind quantum computation is possible for the infinite squeezing case. We also
show that the finite squeezing causes no additional problem in the blind setup
apart from the one inherent to the continuous-variable measurement-based
quantum computation.Comment: 20 pages, 8 figure
Unconditionally verifiable blind computation
Blind Quantum Computing (BQC) allows a client to have a server carry out a
quantum computation for them such that the client's input, output and
computation remain private. A desirable property for any BQC protocol is
verification, whereby the client can verify with high probability whether the
server has followed the instructions of the protocol, or if there has been some
deviation resulting in a corrupted output state. A verifiable BQC protocol can
be viewed as an interactive proof system leading to consequences for complexity
theory. The authors, together with Broadbent, previously proposed a universal
and unconditionally secure BQC scheme where the client only needs to be able to
prepare single qubits in separable states randomly chosen from a finite set and
send them to the server, who has the balance of the required quantum
computational resources. In this paper we extend that protocol with new
functionality allowing blind computational basis measurements, which we use to
construct a new verifiable BQC protocol based on a new class of resource
states. We rigorously prove that the probability of failing to detect an
incorrect output is exponentially small in a security parameter, while resource
overhead remains polynomial in this parameter. The new resource state allows
entangling gates to be performed between arbitrary pairs of logical qubits with
only constant overhead. This is a significant improvement on the original
scheme, which required that all computations to be performed must first be put
into a nearest neighbour form, incurring linear overhead in the number of
qubits. Such an improvement has important consequences for efficiency and
fault-tolerance thresholds.Comment: 46 pages, 10 figures. Additional protocol added which allows
arbitrary circuits to be verified with polynomial securit
Blind quantum computation protocol in which Alice only makes measurements
Blind quantum computation is a new secure quantum computing protocol which
enables Alice who does not have sufficient quantum technology to delegate her
quantum computation to Bob who has a fully-fledged quantum computer in such a
way that Bob cannot learn anything about Alice's input, output, and algorithm.
In previous protocols, Alice needs to have a device which generates quantum
states, such as single-photon states. Here we propose another type of blind
computing protocol where Alice does only measurements, such as the polarization
measurements with a threshold detector. In several experimental setups, such as
optical systems, the measurement of a state is much easier than the generation
of a single-qubit state. Therefore our protocols ease Alice's burden.
Furthermore, the security of our protocol is based on the no-signaling
principle, which is more fundamental than quantum physics. Finally, our
protocols are device independent in the sense that Alice does not need to trust
her measurement device in order to guarantee the security.Comment: 9 pages, 3 figure
Quantum Fully Homomorphic Encryption With Verification
Fully-homomorphic encryption (FHE) enables computation on encrypted data
while maintaining secrecy. Recent research has shown that such schemes exist
even for quantum computation. Given the numerous applications of classical FHE
(zero-knowledge proofs, secure two-party computation, obfuscation, etc.) it is
reasonable to hope that quantum FHE (or QFHE) will lead to many new results in
the quantum setting. However, a crucial ingredient in almost all applications
of FHE is circuit verification. Classically, verification is performed by
checking a transcript of the homomorphic computation. Quantumly, this strategy
is impossible due to no-cloning. This leads to an important open question: can
quantum computations be delegated and verified in a non-interactive manner? In
this work, we answer this question in the affirmative, by constructing a scheme
for QFHE with verification (vQFHE). Our scheme provides authenticated
encryption, and enables arbitrary polynomial-time quantum computations without
the need of interaction between client and server. Verification is almost
entirely classical; for computations that start and end with classical states,
it is completely classical. As a first application, we show how to construct
quantum one-time programs from classical one-time programs and vQFHE.Comment: 30 page
Implementing summative assessment with a formative flavour: a case study in a large class
Teaching a large class can present real challenges in design, management, and standardization of assessment practices. One of the main dilemmas for university teachers is how to implement effective formative assessment practices, with accompanied high quality feedback consistently over time with large classroom groups. This article reports on how elements of formative practices can be implemented as part of summative assessment in very large undergraduate cohorts (n = 1500 in one semester), studying in different modes (on- and off-campus), with multiple markers, and under common cost and time constraints. Design features implemented include the use of exemplars, rubrics and audio feedback. The article draws on the reflections of the leading teacher, and discusses that for summative assessment to benefit learners, it should contain formative assessment elements. The teaching practices utilised in the case study provide some means to resolve the tensions between formative assessment and summative assessment that may be more generally applicable
Superhydrophobicity can enhance convective heat transfer in pressure-driven pipe flow
Theoretical evidence is given that it is possible for superhydrophobicity to enhance steady laminar convective heat transfer in pressure-driven flow along a circular pipe or tube with constant heat flux. Superhydrophobicity here refers to the presence of adiabatic no-shear zones in an otherwise solid no-slip boundary. Adding such adiabatic no-shear zones reduces not only hydrodynamic friction, leading to greater fluid volume fluxes for a given pressure gradient, but also reduces the solid surface area through which heat enters the fluid. This leads to a delicate trade-off between competing mechanisms so that the net effect on convective heat transfer along the pipe, as typically measured by a Nusselt number, is not obvious. Existing evidence in the literature suggests that superhydrophobicity always decreases the Nusselt number, and therefore compromises the net heat transfer. In this theoretical study, we confirm this to be generally true but, significantly, we identify a situation where the opposite occurs and the Nusselt number increases thereby enhancing convective heat transfer along the pipe
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