270 research outputs found
Environment-assisted quantum transport in a 10-qubit network
The way in which energy is transported through an interacting system governs
fundamental properties in many areas of physics, chemistry, and biology.
Remarkably, environmental noise can enhance the transport, an effect known as
environment-assisted quantum transport (ENAQT). In this paper, we study ENAQT
in a network of coupled spins subject to engineered static disorder and
temporally varying dephasing noise. The interacting spin network is realized in
a chain of trapped atomic ions and energy transport is represented by the
transfer of electronic excitation between ions. With increasing noise strength,
we observe a crossover from coherent dynamics and Anderson localization to
ENAQT and finally a suppression of transport due to the quantum Zeno effect. We
found that in the regime where ENAQT is most effective the transport is mainly
diffusive, displaying coherences only at very short times. Further, we show
that dephasing characterized by non-Markovian noise can maintain coherences
longer than white noise dephasing, with a strong influence of the spectral
structure on the transport effciency. Our approach represents a controlled and
scalable way to investigate quantum transport in many-body networks under
static disorder and dynamic noise.Comment: Mai
Exploring Large-Scale Entanglement in Quantum Simulation
Entanglement is a distinguishing feature of quantum many-body systems, and
uncovering the entanglement structure for large particle numbers in quantum
simulation experiments is a fundamental challenge in quantum information
science. Here we perform experimental investigations of entanglement based on
the entanglement Hamiltonian, as an effective description of the reduced
density operator for large subsystems. We prepare ground and excited states of
a 1D XXZ Heisenberg chain on a 51-ion programmable quantum simulator and
perform sample-efficient `learning' of the entanglement Hamiltonian for
subsystems of up to 20 lattice sites. Our experiments provide compelling
evidence for a local structure of the entanglement Hamiltonian. This
observation marks the first instance of confirming the fundamental predictions
of quantum field theory by Bisognano and Wichmann, adapted to lattice models
that represent correlated quantum matter. The reduced state takes the form of a
Gibbs ensemble, with a spatially-varying temperature profile as a signature of
entanglement. Our results also show the transition from area to volume-law
scaling of Von Neumann entanglement entropies from ground to excited states. As
we venture towards achieving quantum advantage, we anticipate that our findings
and methods have wide-ranging applicability to revealing and understanding
entanglement in many-body problems with local interactions including higher
spatial dimensions.Comment: 14 pages, 7 figure
Compatibility and noncontextuality for sequential measurements
A basic assumption behind the inequalities used for testing noncontextual
hidden variable models is that the observables measured on the same individual
system are perfectly compatible. However, compatibility is not perfect in
actual experiments using sequential measurements. We discuss the resulting
"compatibility loophole" and present several methods to rule out certain hidden
variable models which obey a kind of extended noncontextuality. Finally, we
present a detailed analysis of experimental imperfections in a recent trapped
ion experiment and apply our analysis to that case.Comment: 15 pages, 2 figures, v2: problem with latex solve
Observation of magnon bound states in the long-range, anisotropic Heisenberg model
Over the recent years coherent, time-periodic modulation has been established
as a versatile tool for realizing novel Hamiltonians. Using this approach,
known as Floquet engineering, we experimentally realize a long-ranged,
anisotropic Heisenberg model with tunable interactions in a trapped ion quantum
simulator. We demonstrate that the spectrum of the model contains not only
single magnon excitations but also composite magnon bound states. For the
long-range interactions with the experimentally realized power-law exponent,
the group velocity of magnons is unbounded. Nonetheless, for sufficiently
strong interactions we observe bound states of these unconventional magnons
which possess a non-diverging group velocity. By measuring the configurational
mutual information between two disjoint intervals, we demonstrate the
implications of the bound state formation on the entanglement dynamics of the
system. Our observations provide key insights into the peculiar role of
composite excitations in the non-equilibrium dynamics of quantum many-body
systems
Ultraviolet laser pulses with multigigahertz repetition rate and multiwatt average power for fast trapped-ion entanglement operations
The conventional approach to perform two-qubit gate operations in trapped ions relies on exciting the ions on motional sidebands with laser light, which is an inherently slow process. One way to implement a fast entangling gate protocol requires a suitable pulsed laser to increase the gate speed by orders of magnitude. However, the realization of such a fast entangling gate operation presents a big technical challenge, as such the required laser source is not available off-the-shelf. For this, we have engineered an ultrafast entangling gate source based on a frequency comb. The source generates bursts of several hundred mode-locked pulses with pulse energy ∼800 pJ at 5 GHz repetition rate at 393.3 nm and complies with all requirements for implementing a fast two-qubit gate operation. Using a single, chirped ultraviolet pulse, we demonstrate a rapid adiabatic passage in a Ca+ ion. To verify the applicability and projected performance of the laser system for inducing entangling gates we run simulations based on our source parameters. The gate time can be faster than a trap period with an error approaching 10−4
Sideband Thermometry of Ion Crystals
Coulomb crystals of cold trapped ions are a leading platform for the realization of quantum processors and quantum simulations and, in quantum metrology, for the construction of optical atomic clocks and for fundamental tests of the standard model. For these applications, it is not only essential to cool the ion crystal in all its degrees of freedom down to the quantum ground state but also to be able to determine its temperature with a high accuracy. However, when a large ground-state cooled crystal is interrogated for thermometry, complex many-body interactions take place, making it challenging to accurately estimate the temperature with established techniques. In this work, we present a new thermometry method tailored for ion crystals. The method is applicable to all normal modes of motion and does not suffer from a computational bottleneck when applied to large ion crystals. We test the temperature estimate with two experiments, namely with a one-dimensional linear chain of four ions and a two-dimensional crystal of 19 ions and verify the results, where possible, using other methods. The results show that the new method is an accurate and efficient tool for thermometry of ion crystals
Sideband thermometry of ion crystals
Coulomb crystals of cold trapped ions are a leading platform for the
realisation of quantum processors and quantum simulations and, in quantum
metrology, for the construction of optical atomic clocks and for fundamental
tests of the Standard Model. For these applications, it is not only essential
to cool the ion crystal in all its degrees of freedom down to the quantum
ground state, but also to be able to determine its temperature with a high
accuracy. However, when a large ground-state cooled crystal is interrogated for
thermometry, complex many-body interactions take place, making it challenging
to accurately estimate the temperature with established techniques. In this
work we present a new thermometry method tailored for ion crystals. The method
is applicable to all normal modes of motion and does not suffer from a
computational bottleneck when applied to large ion crystals. We test the
temperature estimate with two experiments, namely with a 1D linear chain of 4
ions and a 2D crystal of 19 ions and verify the results, where possible, using
other methods. The results show that the new method is an accurate and
efficient tool for thermometry of ion crystals.Comment: 12+5 pages, 9+2 figures, Fig.3(b) was correcte
Motional state analysis of a trapped ion by ultra-narrowband composite pulses
In this work, we present a method for measuring the motional state of a
two-level system coupled to a harmonic oscillator. Our technique uses
ultra-narrowband composite pulses on the blue sideband transition to scan
through the populations of the different motional states. Our approach does not
assume any previous knowledge of the motional state distribution and is easily
implemented. It is applicable both inside and outside of the Lamb-Dicke regime.
For higher phonon numbers especially, the composite pulse sequence can be used
as a filter for measuring phonon number ranges. We demonstrate this measurement
technique using a single trapped ion and show good detection results with the
numerically evaluated pulse sequence.Comment: 8 pages, 7 figure
An Open-System Quantum Simulator with Trapped Ions
The control of quantum systems is of fundamental scientific interest and
promises powerful applications and technologies. Impressive progress has been
achieved in isolating the systems from the environment and coherently
controlling their dynamics, as demonstrated by the creation and manipulation of
entanglement in various physical systems. However, for open quantum systems,
engineering the dynamics of many particles by a controlled coupling to an
environment remains largely unexplored. Here we report the first realization of
a toolbox for simulating an open quantum system with up to five qubits. Using a
quantum computing architecture with trapped ions, we combine multi-qubit gates
with optical pumping to implement coherent operations and dissipative
processes. We illustrate this engineering by the dissipative preparation of
entangled states, the simulation of coherent many-body spin interactions and
the quantum non-demolition measurement of multi-qubit observables. By adding
controlled dissipation to coherent operations, this work offers novel prospects
for open-system quantum simulation and computation.Comment: Pre-review submission to Nature. For an updated and final version see
publication. Manuscript + Supplementary Informatio
- …