320 research outputs found
Interfering trajectories in experimental quantum-enhanced stochastic simulation
Simulations of stochastic processes play an important role in the
quantitative sciences, enabling the characterisation of complex systems. Recent
work has established a quantum advantage in stochastic simulation, leading to
quantum devices that execute a simulation using less memory than possible by
classical means. To realise this advantage it is essential that the memory
register remains coherent, and coherently interacts with the processor,
allowing the simulator to operate over many time steps. Here we report a
multi-time-step experimental simulation of a stochastic process using less
memory than the classical limit. A key feature of the photonic quantum
information processor is that it creates a quantum superposition of all
possible future trajectories that the system can evolve into. This
superposition allows us to introduce, and demonstrate, the idea of comparing
statistical futures of two classical processes via quantum interference. We
demonstrate interference of two 16-dimensional quantum states, representing
statistical futures of our process, with a visibility of 0.96 0.02.Comment: 9 pages, 5 figure
Single-shot quantum memory advantage in the simulation of stochastic processes
Stochastic processes underlie a vast range of natural and social phenomena.
Some processes such as atomic decay feature intrinsic randomness, whereas other
complex processes, e.g. traffic congestion, are effectively probabilistic
because we cannot track all relevant variables. To simulate a stochastic
system's future behaviour, information about its past must be stored and thus
memory is a key resource. Quantum information processing promises a memory
advantage for stochastic simulation that has been validated in recent
proof-of-concept experiments. Yet, in all past works, the memory saving would
only become accessible in the limit of a large number of parallel simulations,
because the memory registers of individual quantum simulators had the same
dimensionality as their classical counterparts. Here, we report the first
experimental demonstration that a quantum stochastic simulator can encode the
relevant information in fewer dimensions than any classical simulator, thereby
achieving a quantum memory advantage even for an individual simulator. Our
photonic experiment thus establishes the potential of a new, practical resource
saving in the simulation of complex systems
Inferring Transmission Bottleneck Size from Viral Sequence Data Using a Novel Haplotype Reconstruction Method
The transmission bottleneck is defined as the number of viral particles that transmit from one host to establish an infection in another. Genome sequence data have been used to evaluate the size of the transmission bottleneck between humans infected with the influenza virus; however, the methods used to make these estimates have some limitations. Specifically, viral allele frequencies, which form the basis of many calculations, may not fully capture a process which involves the transmission of entire viral genomes. Here, we set out a novel approach for inferring viral transmission bottlenecks; our method combines an algorithm for haplotype reconstruction with maximum likelihood methods for bottleneck inference. This approach allows for rapid calculation and performs well when applied to data from simulated transmission events; errors in the haplotype reconstruction step did not adversely affect inferences of the population bottleneck. Applied to data from a previous household transmission study of influenza A infection, we confirm the result that the majority of transmission events involve a small number of viruses, albeit with slightly looser bottlenecks being inferred, with between 1 and 13 particles transmitted in the majority of cases. While influenza A transmission involves a tight population bottleneck, the bottleneck is not so tight as to universally prevent the transmission of within-host viral diversity. IMPORTANCE Viral populations undergo a repeated cycle of within-host growth followed by transmission. Viral evolution is affected by each stage of this cycle. The number of viral particles transmitted from one host to another, known as the transmission bottleneck, is an important factor in determining how the evolutionary dynamics of the population play out, restricting the extent to which the evolved diversity of the population can be passed from one host to another. Previous study of viral sequence data has suggested that the transmission bottleneck size for influenza A transmission between human hosts is small. Reevaluating these data using a novel and improved method, we largely confirm this result, albeit that we infer a slightly higher bottleneck size in some cases, of between 1 and 13 virions. While a tight bottleneck operates in human influenza transmission, it is not extreme in nature; some diversity can be meaningfully retained between hosts.Peer reviewe
Role of surgical hyoid bone repositioning in modifying upper airway collapsibility
Background: Surgical hyoid bone repositioning procedures are being performed to treat obstructive sleep apnea (OSA), though outcomes are highly variable. This is likely due to lack of knowledge regarding the precise influence of hyoid bone position on upper airway patency. The aim of this study is to determine the effect of surgical hyoid bone repositioning on upper airway collapsibility.Methods: Seven anaesthetized, male, New Zealand White rabbits were positioned supine with head/neck position controlled. The rabbit’s upper airway was surgically isolated and hyoid bone exposed to allow manipulation of its position using a custom-made device. A sealed facemask was fitted over the rabbit’s snout, and mask/upper airway pressures were monitored. Collapsibility was quantified using upper airway closing pressure (Pclose). The hyoid bone was repositioned within the mid-sagittal plane from 0 to 5 mm (1 mm increments) in anterior, cranial, caudal, anterior-cranial (45°) and anterior-caudal (45°) directions.Results: Anterior displacement of the hyoid bone resulted in the greatest decrease in Pclose amongst all directions (p = 0.002). Pclose decreased progressively with each increment of anterior hyoid bone displacement, and down by −4.0 ± 1.3 cmH2O at 5 mm. Cranial and caudal hyoid bone displacement did not alter Pclose (p > 0.35). Anterior-cranial and anterior-caudal hyoid bone displacements decreased Pclose significantly (p < 0.004) and at similar magnitudes to the anterior direction (p > 0.68).Conclusion: Changes in upper airway collapsibility following hyoid bone repositioning are both direction and magnitude dependent. Anterior-based repositioning directions have the greatest impact on reducing upper airway collapsibility, with no effect on collapsibility by cranial and caudal directions. Findings may have implications for guiding and improving the outcomes of surgical hyoid interventions for the treatment of OSA
Testing the reality of Wigner's friend's observations
Does quantum theory apply at all scales, including that of observers? A
resurgence of interest in the long-standing Wigner's friend paradox has shed
new light on this fundamental question. Here---building on a scenario with two
separated but entangled "friends" introduced by Brukner---we rigorously prove
that if quantum evolution is controllable on the scale of an observer, then one
of the following three assumptions must be false: "No-Superdeterminism",
"Locality", or "Absoluteness of Observed Events" (i.e. that every observed
event exists absolutely, not relatively). We show that although the violation
of Bell-type inequalities in such scenarios is not in general sufficient to
demonstrate the contradiction between those assumptions, new inequalities can
be derived, in a theory-independent manner, which are violated by quantum
correlations. We demonstrate this in a proof-of-principle experiment where a
photon's path is deemed an observer. We discuss how this new theorem places
strictly stronger constraints on quantum reality than Bell's theorem.Comment: In v1, v2 we claimed to give the first rigorous proof of Brukner's
theorem, interpreting his "Observer Independent Facts" assumption to be
weaker than what he formalized. This was inaccurate (Brukner's theorem
follows from his assumptions) and obscured the significantly stronger
implications of our theorem. In v3 we name the weaker assumption in our
theorem "Absoluteness of Observed Events
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
Nonlocality activation in a photonic quantum network
Bell nonlocality refers to correlations between two distant, entangled
particles that challenge classical notions of local causality. Beyond its
foundational significance, nonlocality is crucial for device-independent
technologies like quantum key distribution and randomness generation.
Nonlocality quickly deteriorates in the presence of noise, and restoring
nonlocal correlations requires additional resources. These often come in the
form of many instances of the input state and joint measurements, incurring a
significant resource overhead. Here, we experimentally demonstrate that single
copies of Bell-local states, incapable of violating any standard Bell
inequality, can give rise to nonlocality after being embedded into a quantum
network of multiple parties. We subject the initial entangled state to a
quantum channel that broadcasts part of the state to two independent receivers
and certify the nonlocality in the resulting network by violating a tailored
Bell-like inequality. We obtain these results without making any assumptions
about the prepared states, the quantum channel, or the validity of quantum
theory. Our findings have fundamental implications for nonlocality and enable
the practical use of nonlocal correlations in real-world applications, even in
scenarios dominated by noise.Comment: Main text and Supplementary Information. Comments welcom
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