42 research outputs found
Deterministic quantum teleportation of photonic quantum bits by a hybrid technique
Quantum teleportation allows for the transfer of arbitrary, in principle,
unknown quantum states from a sender to a spatially distant receiver, who share
an entangled state and can communicate classically. It is the essence of many
sophisticated protocols for quantum communication and computation. In order to
realize flying qubits in these schemes, photons are an optimal choice, however,
teleporting a photonic qubit has been limited due to experimental
inefficiencies and restrictions. Major disadvantages have been the
fundamentally probabilistic nature of linear-optics Bell measurements as well
as the need for either destroying the teleported qubit or attenuating the input
qubit when the detectors do not resolve photon numbers. Here we experimentally
realize fully deterministic, unconditional quantum teleportation of photonic
qubits. The key element is to make use of a "hybrid" technique:
continuous-variable (CV) teleportation of a discrete-variable, photonic qubit.
By optimally tuning the receiver's feedforward gain, the CV teleporter acts as
a pure loss channel, while the input dual-rail encoded qubit, based on a single
photon, represents a quantum error detection code against amplitude damping and
hence remains completely intact for most teleportation events. This allows for
a faithful qubit transfer even with imperfect CV entangled states: the overall
transfer fidelities range from 0.79 to 0.82 for four distinct qubits, all of
them exceeding the classical limit of teleportation. Furthermore, even for a
relatively low level of the entanglement, qubits are teleported much more
efficiently than in previous experiments, albeit post-selectively (taking into
account only the qubit subspaces), with a fidelity comparable to the previously
reported values
Complete temporal mode characterization of non-Gaussian states by dual homodyne measurement
Optical quantum states defined in temporal modes, especially non-Gaussian
states like photon-number states, play an important role in quantum computing
schemes. In general, the temporal-mode structures of these states are
characterized by one or more complex functions called temporal-mode functions
(TMFs). Although we can calculate TMF theoretically in some cases, experimental
estimation of TMF is more advantageous to utilize the states with high purity.
In this paper, we propose a method to estimate complex TMFs. This method can be
applied not only to arbitrary single-temporal-mode non-Gaussian states but also
to two-temporal-mode states containing two photons. This method is implemented
by continuous-wave (CW) dual homodyne measurement and doesn't need prior
information of the target states nor state reconstruction procedure. We
demonstrate this method by analyzing several experimentally created
non-Gaussian states
Time-domain Ramsey interferometry with interacting Rydberg atoms
We theoretically investigate the dynamics of a gas of strongly interacting
Rydberg atoms subject to a time-domain Ramsey interferometry protocol. The
many-body dynamics is governed by an Ising-type Hamiltonian with long range
interactions of tunable strength. We analyze and model the contrast degradation
and phase accumulation of the Ramsey signal and identify scaling laws for
varying interrogation times, ensemble densities, and ensemble dimensionalities.Comment: 16 pages, 3 figure
Time-Domain Universal Linear-Optical Operations for Universal Quantum Information Processing
We demonstrate universal and programmable three-mode linear optical
operations in the time domain by realizing a scalable dual-loop optical circuit
suitable for universal quantum information processing (QIP). The
programmability, validity, and deterministic operation of our circuit are
demonstrated by performing nine different three-mode operations on
squeezed-state pulses, fully characterizing the outputs with variable
measurements, and confirming their entanglement. Our circuit can be scaled up
just by making the outer loop longer and also extended to universal quantum
computers by incorporating feedforward systems. Thus, our work paves the way to
large-scale universal optical QIP