22 research outputs found
Realization of universal nonadiabatic geometric control on decoherence-free qubits in the XY model
A fundamental requirement of quantum information processing is the protection
from the adverse effects of decoherence and noise. Decoherence-free subspaces
and geometric processing are important steps of quantum information protection.
Here, we provide a new experimentally feasible scheme to combine
decoherence-free subspaces with nonadiabatic geometric manipulations to attain
a universal quantum computation. The proposed scheme is different from previous
proposals and is based on the typical XY interaction coupling, which can be set
up in various nano-engineered systems and therefore open up for realization of
nonadiabatic holonomic quantum computation in decoherence-free subspaces.Comment: 21 pages, 5 figure
Non-Abelian quantum holonomy of hydrogen-like atoms
We study the Uhlmann holonomy [Rep. Math. Phys. 24, 229 (1986)] of quantum
states for hydrogen-like atoms where the intrinsic spin and orbital angular
momentum are coupled by the spin-orbit interaction and subject to a slowly
varying magnetic field. We show that the holonomy for the orbital angular
momentum and spin subsystems is non-Abelian, while the holonomy of the whole
system is Abelian. Quantum entanglement in the states of the whole system is
crucially related to the non-Abelian gauge structure of the subsystems. We
analyze the phase of the Wilson loop variable associated with the Uhlmann
holonomy, and find a relation between the phase of the whole system with
corresponding marginal phases. Based on the result for the model system we
provide evidence that the phase of the Wilson loop variable and the mixed-state
geometric phase [E. Sj\"oqvist {\it et al.} Phys. Rev. Lett. 85, 2845 (2000)]
are in general inequivalent.Comment: Shortened version; journal reference adde
Non-Abelian off-diagonal geometric phases in nano-engineered four-qubit systems
The concept of off-diagonal geometric phase (GP) has been introduced in order
to recover interference information about the geometry of quantal evolution
where the standard GPs are not well-defined. In this Letter, we propose a
physical setting for realizing non-Abelian off-diagonal GPs. The proposed
non-Abelian off-diagonal GPs can be implemented in a cyclic chain of four
qubits with controllable nearest-neighbor interactions. Our proposal seems to
be within reach in various nano-engineered systems and therefore opens up for
first experimental test of the non-Abelian off-diagonal GP.Comment: Some changes, journal reference adde
Temperature-anisotropy conjugate magnon squeezing in antiferromagnets
Quantum squeezing is an essential asset in the field of quantum science and
technology. In this study, we investigate the impact of temperature and
anisotropy on squeezing of quantum fluctuations in two-mode magnon states
within uniaxial antiferromagnetic materials. Through our analysis, we discover
that the inherent nonlinearity in these bipartite magnon systems gives rise to
a conjugate magnon squeezing effect across all energy eigenbasis states, driven
by temperature and anisotropy. We show that temperature induces amplitude
squeezing, whereas anisotropy leads to phase squeezing. In addition, we observe
that the two-mode squeezing characteristic of magnon eigenenergy states is
associated with amplitude squeezing. This highlights the constructive impact of
temperature and the destructive impact of anisotropy on two-mode magnon
squeezing. Nonetheless, our analysis shows that the destructive effect of
anisotropy is bounded. We demonstrate this by showing that, at a given
temperature, the squeezing of the momentum (phase) quadrature (or equivalently,
the stretching of the position (amplitude) quadrature) approaches a constant
function of anisotropy after a finite value of anisotropy. Moreover, our study
demonstrates that higher magnon squeeze factors can be achieved at higher
temperatures, smaller levels of anisotropy, and closer to the Brillouin zone
center. All these characteristics are specific to low-energy magnons in the
uniaxial antiferromagnetic materials that we examine here
Tunable and robust room-temperature magnon-magnon entanglement
Although challenging, realizing controllable high-temperature entanglement is
of immense importance for practical applications as well as for fundamental
research in quantum technologies. Here, we report the existence of entangled
steady states in bipartite quantum magnonic systems at high temperatures. We
consider dissipative dynamics of two magnons in a bipartite antiferromagnet or
ferrimagnet subjected to a vibrational phonon mode and an external rotating
magnetic field. To quantify the bipartite magnon-magnon entanglement, we use
the entanglement negativity and compute its dependence on the temperature and
magnetic field. We show that, for any given phonon frequency and magnon-phonon
coupling rates, there are always ranges of the magnetic field amplitudes and
frequencies, for which bipartite magnon-magnon entanglement persists up to and
above the room temperature. The generality of the result allows for
experimental observation in a variety of crystals and synthetic bipartite
antiferromagnetic and ferrimagnetic materials.Comment: 6 pages, 5 figure
Technologies photoniques avancees appliquees aux procedes industriels et a la mesure Tokyo, 8 novembre 1999
SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : Y 32724 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueMinistere des Affaires Etrangeres, 75 - Paris (France). Direction de la Cooperation Scientifique, Universitaire et de Recherche; Ambassade de France, Tokyo (Japan)FRFranc