40 research outputs found
Digital quantum simulation of spin models with circuit quantum electrodynamics
Systems of interacting quantum spins show a rich spectrum of quantum phases
and display interesting many-body dynamics. Computing characteristics of even
small systems on conventional computers poses significant challenges. A quantum
simulator has the potential to outperform standard computers in calculating the
evolution of complex quantum systems. Here, we perform a digital quantum
simulation of the paradigmatic Heisenberg and Ising interacting spin models
using a two transmon-qubit circuit quantum electrodynamics setup. We make use
of the exchange interaction naturally present in the simulator to construct a
digital decomposition of the model-specific evolution and extract its full
dynamics. This approach is universal and efficient, employing only resources
which are polynomial in the number of spins and indicates a path towards the
controlled simulation of general spin dynamics in superconducting qubit
platforms.Comment: 12 pages, 9 figure
Third ventriculostomy through the lamina terminalis for intracranial pressure monitoring after aneurysm surgery: technical note
Repeated Quantum Error Detection in a Surface Code
The realization of quantum error correction is an essential ingredient for
reaching the full potential of fault-tolerant universal quantum computation.
Using a range of different schemes, logical qubits can be redundantly encoded
in a set of physical qubits. One such scalable approach is based on the surface
code. Here we experimentally implement its smallest viable instance, capable of
repeatedly detecting any single error using seven superconducting qubits, four
data qubits and three ancilla qubits. Using high-fidelity ancilla-based
stabilizer measurements we initialize the cardinal states of the encoded
logical qubit with an average logical fidelity of 96.1%. We then repeatedly
check for errors using the stabilizer readout and observe that the logical
quantum state is preserved with a lifetime and coherence time longer than those
of any of the constituent qubits when no errors are detected. Our demonstration
of error detection with its resulting enhancement of the conditioned logical
qubit coherence times in a 7-qubit surface code is an important step indicating
a promising route towards the realization of quantum error correction in the
surface code.Comment: 12 pages, 11 figure
Predictors and outcomes of shunt-dependent hydrocephalus in patients with aneurysmal sub-arachnoid hemorrhage
Challenging local realism with human choices
A Bell test is a randomized trial that compares experimental observations against the philosophical worldview of local realism 1, in which the properties of the physical world are independent of our observation of them and no signal travels faster than light. A Bell test requires spatially distributed entanglement, fast and high-efficiency detection and unpredictable measurement settings 2,3 . Although technology can satisfy the first two of these requirements 4-7, the use of physical devices to choose settings in a Bell test involves making assumptions about the physics that one aims to test. Bell himself noted this weakness in using physical setting choices and argued that human 'free will' could be used rigorously to ensure unpredictability in Bell tests 8 . Here we report a set of local-realism tests using human choices, which avoids assumptions about predictability in physics. We recruited about 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable selections and illustrates Bell-test methodology 9 . The participants generated 97,347,490 binary choices, which were directed via a scalable web platform to 12 laboratories on five continents, where 13 experiments tested local realism using photons 5,6, single atoms 7, atomic ensembles 10 and superconducting devices 11 . Over a 12-hour period on 30 November 2016, participants worldwide provided a sustained data flow of over 1,000 bits per second to the experiments, which used different human-generated data to choose each measurement setting. The observed correlations strongly contradict local realism and other realistic positions in bipartite and tripartite 12 scenarios. Project outcomes include closing the 'freedom-of-choice loophole' (the possibility that the setting choices are influenced by 'hidden variables' to correlate with the particle properties 13 ), the utilization of video-game methods 14 for rapid collection of human-generated randomness, and the use of networking techniques for global participation in experimental science
Challenging local realism with human choices
A Bell test is a randomized trial that compares experimental observations
against the philosophical worldview of local realism. A Bell test requires
spatially distributed entanglement, fast and high-efficiency detection and
unpredictable measurement settings. Although technology can satisfy the first
two of these requirements, the use of physical devices to choose settings in a
Bell test involves making assumptions about the physics that one aims to test.
Bell himself noted this weakness in using physical setting choices and argued
that human `free will' could be used rigorously to ensure unpredictability in
Bell tests. Here we report a set of local-realism tests using human choices,
which avoids assumptions about predictability in physics. We recruited about
100,000 human participants to play an online video game that incentivizes fast,
sustained input of unpredictable selections and illustrates Bell-test
methodology. The participants generated 97,347,490 binary choices, which were
directed via a scalable web platform to 12 laboratories on five continents,
where 13 experiments tested local realism using photons, single atoms, atomic
ensembles, and superconducting devices. Over a 12-hour period on 30 November
2016, participants worldwide provided a sustained data flow of over 1,000 bits
per second to the experiments, which used different human-generated data to
choose each measurement setting. The observed correlations strongly contradict
local realism and other realistic positions in bipartite and tripartite
scenarios. Project outcomes include closing the `freedom-of-choice loophole'
(the possibility that the setting choices are influenced by `hidden variables'
to correlate with the particle properties), the utilization of video-game
methods for rapid collection of human generated randomness, and the use of
networking techniques for global participation in experimental science.Comment: This version includes minor changes resulting from reviewer and
editorial input. Abstract shortened to fit within arXiv limit