158 research outputs found
Nuclear spin squeezing via electric quadrupole interaction
Control over nuclear spin fluctuations is essential for processes that rely
on preserving the quantum state of an embedded system. For this purpose,
squeezing is a viable alternative, so far that has not been properly exploited
for the nuclear spins. Of particular relevance in solids is the electric
quadrupole interaction (QI), which operates on nuclei having spin higher than
1/2. In its general form, QI involves an electric field gradient (EFG)
biaxiality term. Here, we show that as this EFG biaxiality increases, it
enables continuous tuning of single-particle squeezing from the one-axis
twisting to the two-axis countertwisting limits. A detailed analysis of QI
squeezing is provided, exhibiting the intricate consequences of EFG biaxiality.
The initial states over the Bloch sphere are mapped out to identify those
favorable for fast initial squeezing, or for prolonged squeezings. Furthermore,
the evolution of squeezing in the presence of a phase-damping channel and an
external magnetic field are investigated. We observe that dephasing drives
toward an anti-squeezed terminal state, the degree of which increases with the
spin angular momentum. Finally, QI squeezing in the limiting case of a
two-dimensional EFG with a perpendicular magnetic field is discussed, which is
of importance for two-dimensional materials, and the associated beat patterns
in squeezing are revealed.Comment: Published version in contents, 10 pages, 9 figure
Engineering spin squeezing in a 3D optical lattice with interacting spin-orbit-coupled fermions
One of the most important tasks in modern quantum science is to coherently
control and entangle many-body systems, and to subsequently use these systems
to realize powerful quantum technologies such as quantum-enhanced sensors.
However, many-body entangled states are difficult to prepare and preserve since
internal dynamics and external noise rapidly degrade any useful entanglement.
Here, we introduce a protocol that counterintuitively exploits inhomogeneities,
a typical source of dephasing in a many-body system, in combination with
interactions to generate metrologically useful and robust many-body entangled
states. Motivated by current limitations in state-of-the-art three-dimensional
(3D) optical lattice clocks (OLCs) operating at quantum degeneracy, we use
local interactions in a Hubbard model with spin-orbit coupling to achieve a
spin-locking effect. In addition to prolonging inter-particle spin coherence,
spin-locking transforms the dephasing effect of spin-orbit coupling into a
collective spin-squeezing process that can be further enhanced by applying a
modulated drive. Our protocol is fully compatible with state-of-the-art 3D OLC
interrogation schemes and may be used to improve their sensitivity, which is
currently limited by the intrinsic quantum noise of independent atoms. We
demonstrate that even with realistic experimental imperfections, our protocol
may generate -- dB of spin squeezing in second with
-- atoms. This capability allows OLCs to enter a new era of
quantum enhanced sensing using correlated quantum states of driven
non-equilibrium systems.Comment: 20 pages, 12 figure
Quantum metrology with nonclassical states of atomic ensembles
Quantum technologies exploit entanglement to revolutionize computing,
measurements, and communications. This has stimulated the research in different
areas of physics to engineer and manipulate fragile many-particle entangled
states. Progress has been particularly rapid for atoms. Thanks to the large and
tunable nonlinearities and the well developed techniques for trapping,
controlling and counting, many groundbreaking experiments have demonstrated the
generation of entangled states of trapped ions, cold and ultracold gases of
neutral atoms. Moreover, atoms can couple strongly to external forces and light
fields, which makes them ideal for ultra-precise sensing and time keeping. All
these factors call for generating non-classical atomic states designed for
phase estimation in atomic clocks and atom interferometers, exploiting
many-body entanglement to increase the sensitivity of precision measurements.
The goal of this article is to review and illustrate the theory and the
experiments with atomic ensembles that have demonstrated many-particle
entanglement and quantum-enhanced metrology.Comment: 76 pages, 40 figures, 1 table, 603 references. Some figures bitmapped
at 300 dpi to reduce file siz
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