91 research outputs found
Versatile Digital GHz Phase Lock for External Cavity Diode Lasers
We present a versatile, inexpensive and simple optical phase lock for
applications in atomic physics experiments. Thanks to all-digital phase
detection and implementation of beat frequency pre-scaling, the apparatus
requires no microwave-range reference input, and permits phase locking at
frequency differences ranging from sub-MHz to 7 GHz (and with minor extension,
to 12 GHz). The locking range thus covers ground state hyperfine splittings of
all alkali metals, which makes this system a universal tool for many
experiments on coherent interaction between light and atoms.Comment: 4.5 pages, 5 figures v3: fixed error in schematic: R10 connects to
other end of C
Multi-partite entanglement detection with non symmetric probing
We show that spin squeezing criteria commonly used for entanglement detection
can be erroneous, if the probe is not symmetric. We then derive a lower bound
on squeezing for separable states in spin systems probed asymmetrically. Using
this we further develop a procedure that allows us to verify the degree of
entanglement of a quantum state in the spin system. Finally, we apply our
method for entanglement verification to existing experimental data, and use it
to prove the existence of tri-partite entanglement in a spin squeezed atomic
ensemble.Comment: 7 pages, 2 figures (Include Supplemental material
Photons as quasi-charged particles
The Schrodinger motion of a charged quantum particle in an electromagnetic
potential can be simulated by the paraxial dynamics of photons propagating
through a spatially inhomogeneous medium. The inhomogeneity induces geometric
effects that generate an artificial vector potential to which signal photons
are coupled. This phenomenon can be implemented with slow light propagating
through an a gas of double-Lambda atoms in an electromagnetically-induced
transparency setting with spatially varied control fields. It can lead to a
reduced dispersion of signal photons and a topological phase shift of
Aharonov-Bohm type
Quantum memory for squeezed light
We produce a 600-ns pulse of 1.86-dB squeezed vacuum at 795 nm in an optical
parametric amplifier and store it in a rubidium vapor cell for 1 us using
electromagnetically induced transparency. The recovered pulse, analyzed using
time-domain homodyne tomography, exhibits up to 0.21+-0.04 dB of squeezing. We
identify the factors leading to the degradation of squeezing and investigate
the phase evolution of the atomic coherence during the storage interval.Comment: To appear in PRL. Changes to version 3: we present a larger data set
featuring somewhat less squeezing, but also better statistics and a lower
margin of error. Some additional revisions are made in response to the
referees' comment
Raman Adiabatic Transfer of Optical States
We analyze electromagnetically induced transparency and light storage in an
ensemble of atoms with multiple excited levels (multi-Lambda configuration)
which are coupled to one of the ground states by quantized signal fields and to
the other one via classical control fields. We present a basis transformation
of atomic and optical states which reduces the analysis of the system to that
of EIT in a regular 3-level configuration. We demonstrate the existence of dark
state polaritons and propose a protocol to transfer quantum information from
one optical mode to another by an adiabatic control of the control fields
Dipole force free optical control and cooling of nanofiber trapped atoms
The evanescent field surrounding nanoscale optical waveguides offers an efficient interface between light and mesoscopic ensembles of neutral atoms. However, the thermal motion of trapped atoms, combined with the strong radial gradients of the guided light, leads to a time-modulated coupling between atoms and the light mode, thus giving rise to additional noise and motional dephasing of collective states. Here, we present a dipole force free scheme for coupling of the radial motional states, utilizing the strong intensity gradient of the guided mode and demonstrate all-optical coupling of the cesium hyperfine ground states and motional sideband transitions. We utilize this to prolong the trap lifetime of an atomic ensemble by Raman sideband cooling of the radial motion which, to the best of our knowledge, has not been demonstrated in nano-optical structures previously. This Letter points towards full and independent control of internal and external atomic degrees of freedom using guided light modes only
Squeezing of Atomic Quantum Projection Noise
We provide a framework for understanding recent experiments on squeezing of a
collective atomic pseudo-spin, induced by a homodyne measurement on
off-resonant probe light interrogating the atoms. The detection of light
decimates the atomic state distribution and we discuss the conditions under
which the resulting reduced quantum fluctuations are metrologically relevant.
In particular, we consider a dual probe scheme which benefits from a
cancelation of classical common mode noise sources such that quantum
fluctuations from light and atoms are the main contributions to the detected
signal.Comment: Submitted to Journal of Modern Optic
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Purely antiferromagnetic magnetoelectric random access memory
Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics
Purely Antiferromagnetic Magnetoelectric Random Access Memory
Magnetic random access memory schemes employing magnetoelectric coupling to
write binary information promise outstanding energy efficiency. We propose and
demonstrate a purely antiferromagnetic magnetoelectric random access memory
(AF-MERAM) that offers a remarkable 50 fold reduction of the writing threshold
compared to ferromagnet-based counterparts, is robust against magnetic
disturbances and exhibits no ferromagnetic hysteresis losses. Using the
magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal
switching via gate voltage pulses and all-electric readout at room temperature.
As no ferromagnetic component is present in the system, the writing magnetic
field does not need to be pulsed for readout, allowing permanent magnets to be
used. Based on our prototypes of these novel systems, we construct a
comprehensive model of the magnetoelectric selection mechanism in thin films of
magnetoelectric antiferromagnets. We identify that growth induced effects lead
to emergent ferrimagnetism, which is detrimental to the robustness of the
storage. After pinpointing lattice misfit as the likely origin, we provide
routes to enhance or mitigate this emergent ferrimagnetism as desired. Beyond
memory applications, the AF-MERAM concept introduces a general all-electric
interface for antiferromagnets and should find wide applicability in purely
antiferromagnetic spintronics devices.Comment: Main text (4 figures) + supplementary information (7 figures
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