34 research outputs found
Strong unitary and overlap uncertainty relations: theory and experiment
We derive and experimentally investigate a strong uncertainty relation valid
for any unitary operators, which implies the standard uncertainty relation
as a special case, and which can be written in terms of geometric phases. It is
saturated by every pure state of any -dimensional quantum system, generates
a tight overlap uncertainty relation for the transition probabilities of any
pure states, and gives an upper bound for the out-of-time-order
correlation function. We test these uncertainty relations experimentally for
photonic polarisation qubits, including the minimum uncertainty states of the
overlap uncertainty relation, via interferometric measurements of generalised
geometric phases.Comment: 5 pages of main text, 5 pages of Supplemental Material.
Clarifications added in this updated versio
Fidelity estimation of quantum states on a silicon photonic chip
As a measure of the 'closeness' of two quantum states, fidelity plays a
fundamental role in quantum information theory. Fidelity estimation protocols
try to strike a balance between information gleaned from an experiment, and the
efficiency of its implementation, in terms of the number of states consumed by
the protocol. Here we adapt a previously reported optimal state verification
protocol (Phys. Rev. Lett. 120, 170502, 2018) for fidelity estimation of
two-qubit states. We demonstrate the protocol experimentally using a
fully-programmable silicon photonic two-qubit chip. Our protocol outputs
significantly smaller error bars of its point estimate in comparison with
another widely-used estimation protocol, showing a clear step forward in the
ability to estimate the fidelity of quantum states produced by a practical
device
Maximizing precision in saturation-limited absorption measurements
Quantum fluctuations in the intensity of an optical probe is noise which
limits measurement precision in absorption spectroscopy. Increased probe power
can offer greater precision, however, this strategy is often constrained by
sample saturation. Here, we analyse measurement precision for a generalised
absorption model in which we account for saturation and explore its effect on
both classical and quantum probe performance. We present a classical
probe-sample optimisation strategy to maximise precision and find that optimal
probe powers always fall within the saturation regime. We apply our
optimisation strategy to two examples, high-precision Doppler broadened
thermometry and an absorption spectroscopy measurement of Chlorophyll A. We
derive a limit on the maximum precision gained from using a non-classical probe
and find a strategy capable of saturating this bound. We evaluate
amplitude-squeezed light as a viable experimental probe state and find it
capable of providing precision that reaches to within > 85% of the ultimate
quantum limit with currently available technology.Comment: 12 pages and 5 figure
Heralded quantum steering over a high-loss channel
Entanglement is the key resource for many long-range quantum information
tasks, including secure communication and fundamental tests of quantum physics.
These tasks require robust verification of shared entanglement, but performing
it over long distances is presently technologically intractable because the
loss through an optical fiber or free-space channel opens up a detection
loophole. We design and experimentally demonstrate a scheme that verifies
entanglement in the presence of at least dB of added loss,
equivalent to approximately km of telecommunication fiber. Our protocol
relies on entanglement swapping to herald the presence of a photon after the
lossy channel, enabling event-ready implementation of quantum steering. This
result overcomes the key barrier in device-independent communication under
realistic high-loss scenarios and in the realization of a quantum repeater.Comment: 8 pages, 5 figure
Fidelity estimation of quantum states on a silicon photonic chip
As a measure of the 'closeness' of two quantum states, fidelity plays a fundamental role in quantum information theory. Fidelity estimation protocols try to strike a balance between information gleaned from an experiment, and the efficiency of its implementation, in terms of the number of states consumed by the protocol. Here we adapt a previously reported optimal state verification protocol (Phys. Rev. Lett. 120, 170502, 2018) for fidelity estimation of two-qubit states. We demonstrate the protocol experimentally using a fully-programmable silicon photonic two-qubit chip. Our protocol outputs significantly smaller error bars of its point estimate in comparison with another widely-used estimation protocol, showing a clear step forward in the ability to estimate the fidelity of quantum states produced by a practical device
L00L and p00p entanglement
We demonstrate the generation of unbalanced two-photon entanglement in the
Laguerre-Gaussian (LG) transverse-spatial degree-of-freedom, where one photon
carries a fundamental (Gauss) mode and the other a higher-order LG mode with a
non-zero azimuthal () or radial () component. Taking a cue from the
state nomenclature, we call these types of states (L00L) or
-entangled. They are generated by shifting one photon in the LG mode
space and combining it with a second (initially uncorrelated) photon at a
beamsplitter, followed by coincidence detection. In order to verify two-photon
coherence, we demonstrate a two-photon ``twisted'' quantum eraser, where
Hong-Ou-Mandel interference is recovered between two distinguishable photons by
projecting them into a rotated LG superposition basis. Using an entanglement
witness, we find that our generated and states have fidelities of
95.31\% and 89.80\% to their respective ideal maximally entangled states.
Besides being of fundamental interest, this type of entanglement will likely
have a significant impact on tickling the average quantum physicist's funny
bone.Comment: Written for submission to the AVS Quantum Science special issue in
memory of Jon Dowlin
Necessary condition for steerability of arbitrary two-qubit states with loss
Einstein-Podolsky-Rosen steering refers to the quantum phenomenon whereby the
state of a system held by one party can be "steered" into different states at
the will of another, distant, party by performing different local measurements.
Although steering has been demonstrated in a number of experiments involving
qubits, the question of which two-qubit states are steerable remains an open
theoretical problem. Here, we derive a necessary condition for any two-qubit
state to be steerable when the steering party suffers from a given probability
of qubit loss. Our main result finds application in one-way steering
demonstrations that rely upon loss. Specifically, we apply it to a recent
experiment on one-way steering with projective measurements and POVMs, reported
by Wollmann et. al. [Phys. Rev. Lett., 116, 160403 (2016)].Comment: 7 pages, 1 figur
Conclusive experimental demonstration of one-way Einstein-Podolsky-Rosen steering
Einstein-Podolsky-Rosen steering is a quantum phenomenon wherein one party
influences, or steers, the state of a distant party's particle beyond what
could be achieved with a separable state, by making measurements on one half of
an entangled state. This type of quantum nonlocality stands out through its
asymmetric setting, and even allows for cases where one party can steer the
other, but where the reverse is not true. A series of experiments have
demonstrated one-way steering in the past, but all were based on significant
limiting assumptions. These consisted either of restrictions on the type of
allowed measurements, or of assumptions about the quantum state at hand, by
mapping to a specific family of states and analysing the ideal target state
rather than the real experimental state. Here, we present the first
experimental demonstration of one-way steering free of such assumptions. We
achieve this using a new sufficient condition for non-steerability, and,
although not required by our analysis, using a novel source of extremely
high-quality photonic Werner states.Comment: Supplemental Material included in the documen
Ultrasonically assisted deposition of colloidal crystals
Colloidal particles are a versatile physical system which have found uses across a range of applications such as the simulation of crystal kinetics, etch masks for fabrication, and the formation of photonic band-gap structures. Utilization of colloidal particles often requires a means to produce highly ordered, periodic structures. One approach is the use of surface acoustic waves (SAWs) to direct the self-assembly of colloidal particles. Previous demonstrations using standing SAWs were shown to be limited in terms of crystal size and dimensionality. Here, we report a technique to improve the spatial alignment of colloidal particles using traveling SAWs. Through control of the radio frequency power, which drives the SAW, we demonstrate enhanced quality and dimensionality of the crystal growth. We show that this technique can be applied to a range of particle sizes in the 孭regime and may hold potential for particles in the sub-孭regime.Griffith Sciences, School of Natural SciencesFull Tex