10,795 research outputs found
Universal quantum gates between nitrogen-vacancy centers in a levitated nanodiamond
We propose a scheme to realize universal quantum gates between
nitrogen-vacancy (NV) centers in an optically trapped nanodiamond, through
uniform magnetic field induced coupling between the NV centers and the
torsional mode of the levitated nanodiamond. The gates are tolerant to the
thermal noise of the torsional mode. By combining the scheme with dynamical
decoupling technology, it is found that the high fidelity quantum gates are
possible for the present experimental conditions. The proposed scheme is useful
for NV-center-based quantum network and distributed quantum computationComment: 7 pages, 6 figure
State-independent geometric quantum gates via nonadiabatic and noncyclic evolution
Geometric phases are robust to local noises and the nonadiabatic ones can
reduce the evolution time, thus nonadiabatic geometric gates have strong
robustness and can approach high fidelity. However, the advantage of geometric
phase has not being fully explored in previous investigations. Here, we propose
a scheme for universal quantum gates with pure nonadiabatic and noncyclic
geometric phases from smooth evolution paths. In our scheme, only geometric
phase can be accumulated in a fast way, and thus it not only fully utilizes the
local noise resistant property of geometric phase but also reduces the
difficulty in experimental realization. Numerical results show that the
implemented geometric gates have stronger robustness than dynamical gates and
the geometric scheme with cyclic path. Furthermore, we propose to construct
universal quantum gate on superconducting circuits, and the gate fidelity can
be and , respectively. Therefore, these high-fidelity
quantum gates are promising for large-scale fault-tolerant quantum computation
Logic gates at the surface code threshold: Superconducting qubits poised for fault-tolerant quantum computing
A quantum computer can solve hard problems - such as prime factoring,
database searching, and quantum simulation - at the cost of needing to protect
fragile quantum states from error. Quantum error correction provides this
protection, by distributing a logical state among many physical qubits via
quantum entanglement. Superconductivity is an appealing platform, as it allows
for constructing large quantum circuits, and is compatible with
microfabrication. For superconducting qubits the surface code is a natural
choice for error correction, as it uses only nearest-neighbour coupling and
rapidly-cycled entangling gates. The gate fidelity requirements are modest: The
per-step fidelity threshold is only about 99%. Here, we demonstrate a universal
set of logic gates in a superconducting multi-qubit processor, achieving an
average single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up
to 99.4%. This places Josephson quantum computing at the fault-tolerant
threshold for surface code error correction. Our quantum processor is a first
step towards the surface code, using five qubits arranged in a linear array
with nearest-neighbour coupling. As a further demonstration, we construct a
five-qubit Greenberger-Horne-Zeilinger (GHZ) state using the complete circuit
and full set of gates. The results demonstrate that Josephson quantum computing
is a high-fidelity technology, with a clear path to scaling up to large-scale,
fault-tolerant quantum circuits.Comment: 15 pages, 13 figures, including supplementary materia
- …