82 research outputs found
Quantifying high dimensional entanglement with two mutually unbiased bases
We derive a framework for quantifying entanglement in multipartite and high
dimensional systems using only correlations in two unbiased bases. We
furthermore develop such bounds in cases where the second basis is not
characterized beyond being unbiased, thus enabling entanglement quantification
with minimal assumptions. Furthermore, we show that it is feasible to
experimentally implement our method with readily available equipment and even
conservative estimates of physical parameters.Comment: 17 pages, 1 figur
Templates, Crash Test Dummies and Digitalization:: European Models of Man in the Car Industry
Fundamental accuracy-resolution trade-off for timekeeping devices
From a thermodynamic point of view, all clocks are driven by irreversible
processes. Additionally, one can use oscillatory systems to temporally modulate
the thermodynamic flux towards equilibrium. Focusing on the most elementary
thermalization events, this modulation can be thought of as a temporal
probability concentration for these events. There are two fundamental factors
limiting the performance of clocks: On the one level, the inevitable drifts of
the oscillatory system, which are addressed by finding stable atomic or nuclear
transitions that lead to astounding precision of today's clocks. On the other
level, there is the intrinsically stochastic nature of the irreversible events
upon which the clock's operation is based. This becomes relevant when seeking
to maximize a clock's resolution at high accuracy, which is ultimately limited
by the number of such stochastic events per reference time unit. We address
this essential trade-off between clock accuracy and resolution, proving a
universal bound for all clocks whose elementary thermalization events are
memoryless.Comment: 5 + 7 pages, 8 figures, published versio
Deutsche Unternehmer zwischen Kriegswirtschaft und Wiederaufbau. Studien zur Erfahrungsbildung von Industrie-Eliten
The Impact of Imperfect Timekeeping on Quantum Control
In order to unitarily evolve a quantum system, an agent requires knowledge of
time, a parameter which no physical clock can ever perfectly characterise. In
this letter, we study how limitations on acquiring knowledge of time impact
controlled quantum operations in different paradigms. We show that the quality
of timekeeping an agent has access to limits the gate complexity they are able
to achieve within circuit-based quantum computation. It also exponentially
impacts state preparation for measurement-based quantum computation. Another
area where quantum control is relevant is quantum thermodynamics. In that
context, we show that cooling a qubit can be achieved using a timer of
arbitrary quality for control: timekeeping error only impacts the rate of
cooling and not the achievable temperature. Our analysis combines techniques
from the study of autonomous quantum clocks and the theory of quantum channels
to understand the effect of imperfect timekeeping on controlled quantum
dynamics.Comment: 5 + 7 pages, 2 figure
DiVincenzo-like criteria for autonomous quantum machines
Controlled quantum machines have matured significantly. A natural next step
is to grant them autonomy, freeing them from timed external control. For
example, autonomy could unfetter quantum computers from classical control wires
that heat and decohere them; and an autonomous quantum refrigerator recently
reset superconducting qubits to near their ground states, as is necessary
before a computation. What conditions are necessary for realizing useful
autonomous quantum machines? Inspired by recent quantum thermodynamics and
chemistry, we posit conditions analogous to DiVincenzo's criteria for quantum
computing. Our criteria are intended to foment and guide the development of
useful autonomous quantum machines.Comment: 7 pages (2 figures + 1 table) + appendi
Experimental high-dimensional entanglement certification and quantum steering with time-energy measurements
High-dimensional entanglement provides unique ways of transcending the
limitations of current approaches in quantum information processing, quantum
communications based on qubits. The generation of time-frequency qudit states
offer significantly increased quantum capacities while keeping the number of
photons constant, but pose significant challenges regarding the possible
measurements for certification of entanglement. Here, we develop a new scheme
and experimentally demonstrate the certification of 24-dimensional entanglement
and a 9-dimensional quantum steering. We then subject our photon-pairs to
dispersion conditions equivalent to the transmission through 600-km of fiber
and still certify 21-dimensional entanglement. Furthermore, we use a steering
inequality to prove 7-dimensional entanglement in a semi-device independent
manner, proving that large chromatic dispersion is not an obstacle in
distributing and certifying high-dimensional entanglement and quantum steering.
Our highly scalable scheme is based on commercial telecommunication optical
fiber components and recently developed low-jitter high-efficiency
single-photon detectors, thus opening new pathways towards advanced large-scale
quantum information processing and high-performance, noise-tolerant quantum
communications with time-energy measurementsComment: 30 pages, 4 figure
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