106 research outputs found
Optical holonomic single quantum gates with a geometric spin under a zero field
Realization of fast fault-tolerant quantum gates on a single spin is the core
requirement for solid-state quantum-information processing. As polarized light
shows geometric interference, spin coherence is also geometrically controlled
with light via the spin-orbit interaction. Here, we show that a geometric spin
in a degenerate subspace of a spin-1 electronic system under a zero field in a
nitrogen vacancy center in diamond allows implementation of optical
non-adiabatic holonomic quantum gates. The geometric spin under quasi-resonant
light exposure undergoes a cyclic evolution in the spin-orbit space, and
acquires a geometric phase or holonomy that results in rotations about an
arbitrary axis by any angle defined by the light polarization and detuning.
This enables universal holonomic quantum gates with a single operation. We
demonstrate a complete set of Pauli quantum gates using the geometric spin
preparation and readout techniques. The new scheme opens a path to holonomic
quantum computers and repeaters
Dynamical decoupling of a geometric qubit
Quantum bits or qubits naturally decohere by becoming entangled with
uncontrollable environments. Dynamical decoupling is thereby required to
disentangle qubits from an environment by periodically reversing the qubit
bases, but this causes rotation error to accumulate. Whereas a conventional
qubit is rotated within the SU(2) two-level system, a geometric qubit defined
in the degenerate subspace of a V-shaped SU(3) three-level system is
geometrically rotated via the third ancillary level to acquire a geometric
phase. We here demonstrate that, simply by introducing detuning, the dynamical
decoupling of the geometric qubit on a spin triplet electron in a
nitrogen-vacancy center in diamond can be made to spontaneously suppress error
accumulation. The geometric dynamical decoupling extends the coherence time of
the geometric qubit up to 1.9 ms, limited by the relaxation time, with 128
decoupling gates at room temperature. Our technique opens a route to holonomic
quantum memory for use in various quantum applications requiring sequential
operation
Single-photon interference over 150-km transmission using silica-based integrated-optic interferometers for quantum cryptography
We have demonstrated single-photon interference over 150 km using
time-division interferometers for quantum cryptography, which were composed of
two integrated-optic asymmetric Mach-Zehnder interferometers, and balanced
gated-mode photon detectors. The observed fringe visibility was more than 80%
after 150-km transmission.Comment: 10 pages, 2 figures, submitted to Electronics Letter
Four-Photon Quantum Interferometry at a Telecom Wavelength
We report the experimental demonstration of four-photon quantum interference
using telecom-wavelength photons. Realization of multi-photon quantum
interference is essential to linear optics quantum information processing and
measurement-based quantum computing. We have developed a source that
efficiently emits photon pairs in a pure spectrotemporal mode at a telecom
wavelength region, and have demonstrated the quantum interference exhibiting
the reduced fringe intervals that correspond to the reduced de Broglie
wavelength of up to the four photon `NOON' state. Our result should open a path
to practical quantum information processing using telecom-wavelength photons.Comment: 4 pages, 4 figure
- …