61 research outputs found
Blueprint for fault-tolerant quantum computation with Rydberg atoms
We present a blueprint for building a fault-tolerant universal quantum computer with Rydberg atoms. Our scheme, which is based on the surface code, uses individually addressable, optically trapped atoms as qubits and exploits electromagnetically induced transparency to perform the multiqubit gates required for error correction and computation. We discuss the advantages and challenges of using Rydberg atoms to build such a quantum computer, and we perform error correction simulations to obtain an error threshold for our scheme. Our findings suggest that Rydberg atoms are a promising candidate for quantum computation, but gate fidelities need to improve before fault-tolerant universal quantum computation can be achieved
Spacetime-Efficient Low-Depth Quantum State Preparation with Applications
We propose a novel deterministic method for preparing arbitrary quantum
states. When our protocol is compiled into CNOT and arbitrary single-qubit
gates, it prepares an -dimensional state in depth and spacetime
allocation (a metric that accounts for the fact that oftentimes some ancilla
qubits need not be active for the entire circuit) , which are both
optimal. When compiled into the gate set, we show
that it requires asymptotically fewer quantum resources than previous methods.
Specifically, it prepares an arbitrary state up to error in depth
and spacetime allocation ,
improving over and ,
respectively. We illustrate how the reduced spacetime allocation of our
protocol enables rapid preparation of many disjoint states with only
constant-factor ancilla overhead -- ancilla qubits are reused
efficiently to prepare a product state of -dimensional states in depth
rather than , achieving effectively constant
depth per state. We highlight several applications where this ability would be
useful, including quantum machine learning, Hamiltonian simulation, and solving
linear systems of equations. We provide quantum circuit descriptions of our
protocol, detailed pseudocode, and gate-level implementation examples using
Braket
Universal topological phase of 2D stabilizer codes
Two topological phases are equivalent if they are connected by a local
unitary transformation. In this sense, classifying topological phases amounts
to classifying long-range entanglement patterns. We show that all 2D
topological stabilizer codes are equivalent to several copies of one universal
phase: Kitaev's topological code. Error correction benefits from the
corresponding local mappings.Comment: 4 pages, 3 figure
Fault-tolerant protection of near-term trapped-ion topological qubits under realistic noise sources
The quest of demonstrating beneficial quantum error correction in near-term
noisy quantum processors can benefit enormously from a low-resource
optimization of fault-tolerant schemes, which are specially designed for a
particular platform considering both state-of-the-art technological
capabilities and main sources of noise. In this work, we show that
flag-qubit-based fault-tolerant techniques for active error detection and
correction, as well as for encoding of logical qubits, can be leveraged in
current designs of trapped-ion quantum processors to achieve this break-even
point of beneficial quantum error correction. Our improved description of the
relevant sources of noise, together with detailed schedules for the
implementation of these flag-based protocols, provide one of the most complete
microscopic characterizations of a fault-tolerant quantum processor to date. By
extensive numerical simulations, we provide a comparative study of flag- and
cat-based approaches to quantum error correction, and show that the superior
performance of the former can become a landmark in the success of near-term
quantum computing with noisy trapped-ion devices.Comment: new version, accepted in Phys. Rev.
Generalized Toric Codes Coupled to Thermal Baths
We have studied the dynamics of a generalized toric code based on qudits at
finite temperature by finding the master equation coupling the code's degrees
of freedom to a thermal bath. As a consequence, we find that for qutrits new
types of anyons and thermal processes appear that are forbidden for qubits.
These include creation, annihilation and diffusion throughout the system code.
It is possible to solve the master equation in a short-time regime and find
expressions for the decay rates as a function of the dimension of the
qudits. Although we provide an explicit proof that the system relax to the
Gibbs state for arbitrary qudits, we also prove that above a certain crossing
temperature, qutrits initial decay rate is smaller than the original case for
qubits. Surprisingly this behavior only happens with qutrits and not with other
qudits with .Comment: Revtex4 file, color figures. New Journal of Physics' versio
Heavy metal and nitrogen concentrations in mosses are declining across Europe whilst some “hotspots” remain in 2010
In recent decades, naturally growing mosses have been used successfully as biomonitors of atmospheric deposition of heavy metals and nitrogen. Since 1990, the European moss survey has been repeated at five-yearly intervals. In 2010, the lowest concentrations of metals and nitrogen in mosses were generally found in northern Europe, whereas the highest concentrations were observed in (south-)eastern Europe for metals and the central belt for nitrogen. Averaged across Europe, since 1990, the median concentration in mosses has declined the most for lead (77%), followed by vanadium (55%), cadmium (51%), chromium (43%), zinc (34%), nickel (33%), iron (27%), arsenic (21%, since 1995), mercury (14%, since 1995) and copper (11%). Between 2005 and 2010, the decline ranged from 6% for copper to 36% for lead; for nitrogen the decline was 5%. Despite the Europe-wide decline, no changes or increases have been observed between 2005 and 2010 in some (regions of) countries
Structure of 2D Topological Stabilizer Codes
We provide a detailed study of the general structure of two-dimensional
topological stabilizer quantum error correcting codes, including subsystem
codes. Under the sole assumption of translational invariance, we show that all
such codes can be understood in terms of the homology of string operators that
carry a certain topological charge. In the case of subspace codes, we prove
that two codes are equivalent under a suitable set of local transformations if
and only they have equivalent topological charges. Our approach emphasizes
local properties of the codes over global ones.Comment: 54 pages, 11 figures, version accepted in journal, improved
presentation and result
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