and Switching of Cold Atom Streams
Contemporary discussion on the role of
quantum effects in the brain is rather far from the final conclusion. Any study
of quantum effects which have similarity to the human brain functions is
interesting and fruitful. Many new technical solutions and even principles of
computations and artificial intelligence can be found on this way.
This proposed article is on the
electronically controlled techniques of transferring of cold atoms from one stream
to another. The cold atoms are the gaseous matter cooled up to extremely low
temperatures below 1K. In these cases, the thermal movements of atoms are slow
and the quantum nature of matter is brightly seen.
The most studied cold matter is composed
of alkali atoms, and they are controlled by the magnetic or/and electric fields
that form traps in the space. This trapping effect is described by the
effective potential and the Schrödinger equation regarding the probability
density function. Under certain conditions, this cold matter can be in the Bose-Einstein
condensate state when the quantum interactions are rather strong, and the atoms
show the collective behavior. In this case, averaging gives a new equation describing
this effect, and it is the Gross-Pitaevsky equation . The behavior of Bose condensates
is very rich of nonlinear phenomena, and controlling them by the electric
and/or magnetic fields is a very attractive idea that probably would lead to a new
type of computations, controlled spatio-time quantum processes, and even cold
This proposed paper is on the one particular
linear effect for cold matter governed by joint static magnetic (DC) and
radio-frequency (RF) fields. The cold matter from one atom stream is pumped to
another by adiabatically varied fields, and the process is reminiscent the synaptic
effect in living matter.
Potential for Joint RF/DC Excitations of Traps and Atomic Waveguides
More flexibility in the design of spatial
trapping shapes provides the joint DC/RF fields. In the case of strong ones,
the atoms are interacting with a large portion of the electromagnetic field
quanta, and the trapped atoms are in so-called dressed state .
Experimentally, it has been found that the effective potential landscape
depends on the RF frequency, DC and RF fields amplitudes, and the orientation
of the DC and RF fields relative each other . In this case, several
analytical formulas are derived to calculate the effective potential shapes. Thus,
this joint excitation gives more flexibility to form certain potential shapes
than only the DC trap feeding.
Atoms placed in a strong magnetic field
have the splitted energy levels. One of them is the ground state, and the atoms
in this state seek the areas with a strong potential. They can be placed at
higher levels by excitation with the laser light or microwave radiation. Atoms of
some higher states tend to the areas with the decreased potential. In , an
RF/DC Ioffe-Pritchard trap is considered allowing concentration of atoms of
different quantum states in neighboring areas.
Changing the potential slow enough, these
concentrated atoms can be moved from one place to another, and this is the
guiding effect. Additionally, atoms from different spots can be transferred to
the collision area where they can interact with each other and can be placed in
the qubit state. Interacting qubits can be in the special state of a quantum cluster
called entangled state, and this effect is the basic in quantum computations.
3. Wire as an Open
Atomic Trap and Guide
The RF/DC currents along a single wire form
a cylinder like trapping area, and this is the simplest trap . The minimal
value of the trapping potential is zero and additional biasing by the DC or RF
field is in a need to avoid the flip-flop of trapped atoms.
concentrated along the wire can be moved from one place to another by additional
forces. For this purpose, the coaxial-to-the-wire rings are used. The rings
carry the RF and (or) DC currents, and they form a potential minimum at the
given coordinate along the wire. Changing the currents the minimum together
with the cold atom clouds can be moved from one ring to another.
4. Crossed Wires and
In , it was found that perpendicularly
oriented wires of the trap carrying RF and DC currents can form the merged
potential minimums or these minimums can be separated from each other by a
potential barrier. Later, this effect was proposed for controlled atom transfer
from one wire to another  and was studied in the details in .
Fig. 1 shows the
crossed wires when the trapping manifolds are not touching each other. The atom
streams are divided by a potential barrier, and atoms can be moved along the
perpendicularly placed wires independently by variation of the fields from the
minimum manifolds of two crossed wires carrying DC and RF currents
the frequency, the radii of the minimum manifolds are increased, and the trapping
cylinders are touching each other (Fig. 2).
Fig. 2. Merged minimum
In the ideal case,
at the touching point, the effective potential manifold has a typical flower-like
shape shown in Fig. 3. At this point, the atoms can wander from one wire to another,
and this is the quasi-synaptic effect.
Fig. 3. Potential
shape at the crossing point
The atoms can be pumped from one guiding
wire to another by a specially designed procedure or protocol . In this
case, the currents on the driving rings and guiding wires are varied according
to a certain rule. At the first, a common minimum is formed between the donor
vertical wire and horizontal acceptor wire where the atoms from the donor wire
are concentrated (Fig. 4).
Fig. 4. Common
minimum between the donor vertical wire and acceptor (horizontal) one
Then, the minimums are decoupled from each
other, and the atomic cloud is moved along the horizontal wire (Fig. 5)
Fig. 5. Separated
minimums around the wires and the beginning of pumping the cold atoms around
the horizontal acceptor wire
This studied transfer of cold atom matter
is interesting for many applications. The first, it is prescribed delivery of
atoms to the collision area. The second, it is quantum interferometry. The
third, the controlled shaping of the potential allows forming the wanted
potential distributions in the 3-D space and organize the interaction of areas
of cold matter or even Bose-Einstein condensates in a prescribed manner
governed by non-linear Gross-Pitaevsky equations.
The quasi-synaptic effect has been
considered for cold atom streams. The atoms are trapped along crossed wires.
Normally, the cylindrical traps are isolated by a potential barrier. The
trapping manifolds of the effective potential governing the atom movement can
be touched at the cross-point, and a part of the atoms can be moved from one
wire to another by the variation of the biasing and trapping currents. The
found effect is interesting in quantum high-sensitive interferometry,
prescribed atom transportation and shaping the trapping effective potential in the
3D space to register the cold atom clouds.
1. F. DALFOVO et al,
Theory of Bose-Einstein Condensation in Trapped Gases, Rev. Modern Phys.,
71 (1999) 463-512.
2. C. COHEN-TANNUDJI, Manipulating
Atoms with Photons, Rev. Modern Phys., 70, (1998) 707-719.
SCHUMM et al , Matter-wave Interferometry in a Double Well on an Atom
Chip, Nature 1 (2005) 57-62.
4. G.A. KOUZAEV and
K.J. SAND, RF Controllable Ioffe-Pritchard Trap for Cold Dressed Atoms, Modern
Phys. Lett. B 21, (2007) 59-68.
5. G.A. KOUZAEV,
Quantum Synapse for Cold Atoms, Proc. 5th Int. Conf. Physics,
Technology and Applications of Wave Processes, Samara, Russia, 12-14 Sept.,
6. G.A. KOUZAEV and K.J. SAND, Inter-wire Transfer of Cold Dressed Atoms,
Modern Phys. Lett., B 21 (2007) 1653-1665.
Kouzaev and Karl Jakob Sand
of Science and Technology