387 research outputs found
Cross-Kerr nonlinearity in optomechanical systems
We consider the response of a nanomechanical resonator interacting with an
electromagnetic cavity via a radiation pressure coupling and a cross-Kerr
coupling. Using a mean field approach we solve the dynamics of the system, and
show the different corrections coming from the radiation pressure and the
cross-Kerr effect to the usually considered linearized dynamics.Comment: 6 pages, 9 figure
Cross-Kerr nonlinearity for phonon counting
State measurement of a quantum harmonic oscillator is essential in quantum
optics and quantum information processing. In a system of trapped ions, we
experimentally demonstrate the projective measurement of the state of the ions'
motional mode via an effective cross-Kerr coupling to another motional mode.
This coupling is induced by the intrinsic nonlinearity of the Coulomb
interaction between the ions. We spectroscopically resolve the frequency shift
of the motional sideband of the first mode due to presence of single phonons in
the second mode and use it to reconstruct the phonon number distribution of the
second mode.Comment: 5 pages, 3 figure
Distillation of logic-qubit entanglement assisted with cross-Kerr nonlinearity
Logic-qubit entanglement has attracted much attention in both quantum
communication and quantum computation. Here, we present an efficient protocol
to distill the logic-qubit entanglement with the help of cross-Kerr
nonlinearity. This protocol not only can purify the logic bit-flip error and
logic phase-flip error, but also can correct the physical bit-flip error
completely. We use cross-Kerr nonlinearity to construct quantum nondemolition
detectors. Our distillation protocol for logic-qubit entanglement may be useful
for the practical applications in quantum information, especially in
long-distance quantum communication.Comment: 10 pages, 3 figure
Cross-Kerr effective Hamiltonian for a non-resonant four-level atom
We derive a cross-Kerr type effective Hamiltonian for the four-level atom
interacting with three electromagnetic fields in the N-configuration. When the
atom has relaxed into the ground state a cross-Kerr nonlinearity arises between
two weak probe fields. As a development on earlier work we show in general that
the atom will also display a linear and self-Kerr response. However, if certain
resonance conditions are satisfied then the linear and self-Kerr interactions
will vanish. The electrical susceptibilities of the probe transitions are also
explored and it is shown that a large, pure cross-Kerr nonlinearity can be
generated with vanishing absorption of both probe fields.Comment: 7 pages, 4 figures, submitted to Phys. Rev. A, Replacement: added
Acknowledgments sectio
Quantum control gates with weak cross-Kerr nonlinearity
In this paper, with the weak cross-Kerr nonlinearity, we first present a
special experimental scheme called C-path gate with which the realization of
all possible bipartite POVMs of two-photon polarization states can be simpler
and nearly deterministic. Following the same technique, the schemes of the
realization of quantum control gates have been proposed, including the CNOT
gate (1/2), Fredkin gate (1/8), Toffoli gate (2/23), CU gate and even MCU gate.
All these gates are scalable with the certain probabilities which are larger
than those gates in linear optics. Less resource are required and the
structures of these gates are so simple that we think they are feasible with
current technology and may be useful for the realization of universal
computation in optics.Comment: 12 pages, 4 figure
Efficient single-photon entanglement concentration for quantum communications
We present two protocols for the single-photon entanglement concentration.
With the help of the 50:50 beam splitter, variable beam splitter and an
auxiliary photon, we can concentrate a less-entangled single-photon state into
a maximally single-photon entangled state with some probability. The first
protocol is implemented with linear optics and the second protocol is
implemented with the cross-Kerr nonlinearity. Our two protocols do not need two
pairs of entangled states shared by the two parties, which makes our protocols
more economic. Especially, in the second protocol, with the help of the
cross-Kerr nonlinearity, the sophisticated single photon detector is not
required. Moreover, the second protocol can be reused to get higher success
probability. All these advantages may make our protocols useful in the
long-distance quantum communication.Comment: 9 pages, 3 figure
Atom-photon, two-mode entanglement and two-mode squeezing in the presence of cross-Kerr nonlinearity
The interaction of two quantized fields and three-level quantum system in a
lambda-type configuration is investigated in the presence of cross-Kerr
nonlinearity. We consider three models of coupling for the atom-photon
interaction. First, we study the dynamical behavior of the atom-photon
entanglement and show that increasing the cross-Kerr nonlinearity results in
different behaviors in three considered models. Moreover, it is demonstrated
that the two quantized modes can be entangled, on the other hand, by applying a
classical driving field to the lower levels. Increasing the classical driving
field destroys the long time atom-photon entanglement. Our results show that an
oscillatory two-mode squeezing can be generated in the absence of a driving
classical field and the cross-Kerr nonlinearity
Complete nondestructive analysis of two-photon six-qubit hyperentangled Bell states assisted by cross-Kerr nonlinearity
Hyperentanglement, the entanglement in several degrees of freedom (DOFs) of a
quantum system, has attracted much attention as it can be used to increase both
the channel capacity of quantum communication and its security largely. Here,
we present the first scheme to completely distinguish the hyperentangled Bell
states of two-photon systems in three DOFs with the help of cross-Kerr
nonlinearity without destruction, including two longitudinal momentum DOFs and
the polarization DOF. We use cross-Kerr nonlinearity to construct quantum
nondemolition detectors which can be used to make a parity-check measurement
and analyze Bell states of two-photon systems in different DOFs. Our complete
scheme for two-photon six-qubit hyperentangled Bell-state analysis may be
useful for the practical applications in quantum information, especially in
long-distance high-capacity quantum communication.Comment: 11 pages, 5 figures, one colum
One-step direct measurement of the entangled W states with cross-Kerr nonlinearity
We propose a scheme to directly measure the entangled W states with
cross-Kerr nonlinearity mediums. This scheme can measure three-photon,
four-photon, and even N-photon W states in one step. Only PBSs and cross-Kerr
nonlinearity mediums are used in this scheme, which is feasible for
experiments. We describe the three-photon W states measurement process and
extend it to four-photon and N-photon W states.Comment: 8 pages, 3 figure
Amplification and cross-Kerr nonlinearity in waveguide quantum electrodynamics
We explore amplification and cross-Kerr nonlinearity by a three-level emitter
(3LE) embedded in a waveguide and driven by two light beams. The coherent
amplification and cross-Kerr nonlinearity were demonstrated in recent
experiments, respectively, with a V and a ladder-type 3LE coupled to an open
superconducting transmission line carrying two microwave fields. Here, we
consider , V, and ladder-type 3LE, and compare the efficiency of
coherent and incoherent amplification as well as the magnitude of the
cross-Kerr phase shift in all three emitters. We apply the Heisenberg-Langevin
equations approach to investigate the scattering of a probe and a drive beams
both initially in a coherent state. We particularly calculate the regime of the
probe and drive powers when the 3LE acts most efficiently as a coherent
amplifier, and derive the second-order coherence of amplified probe photons.
Finally, we apply the Kramers-Kronig relations to correlate the amplitude and
phase response of the probe beam, which are used in finding the coherent
amplification and the cross-Kerr phase shift in these systems.Comment: 17 pages, 10 figures, published versio
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