# Monthly Archives: January 2013

"I attribute essentially all my success to the very large amount of chocolate that I consume.  Personally I feel that milk chocolate makes you stupid.Now dark chocolate is the way to go. It's one thing if you want like a medicine or chemistry Nobel Prize, OK, but if you want a physics Nobel Prize it pretty much has got to be dark chocolate."

--- Erik Cornell

# History of atomic physics at the University of Nevada, Reno

With the on-going search for an experimental atomic physics faculty at the University of Nevada, Reno (UNR), I would like to provide a historical perspective on strong traditions of atomic physics at UNR.

The early history of atomic physics at UNR is succinctly captured by Hulse, Goodall and Allen in their book  "Reinventing The System: Higher Education In Nevada, 1968-2000".

"The physics faculty began building a solid record in atomic and molecular physics in the 1960s and improved on this foundation into the 1990s; Philip Altick, trained at Stanford and Berkeley, was an academic leader in this field for three decades and is recognized for initiating the department's high research standards. Colleagues Peter Winkler and Reinhard Bruch were attracted to UNR from Germany partly because of the important theoretical work under way here. Ron Phaneuf, department chair through most of the 1990s, was credited with advances in the program during that decade."

While Ron served as Department Chair, he established a program to study photoionization of ions at the Advanced Light Source in Berkeley. During that same period the UNR AMO program also grew. Faculty hires included Rami Ali, a recognized expert in experimental atomic collisions. After spending several years at UNR, Rami  accepted an academic post in his native Jordan. Paul Neill collaborated on electron beam ion trap physics at Lawrence Livermore National Labotratory. Jeff Thompson has made important progress in measuring properties of negative ions and maintains that research program while serving as the Dean of College of Science at UNR.

Following Philip Altick’s retirement, a theorist, Andrei Derevianko, was hired. Andrei's interests are broad but primarily are in atomic clocks and in connecting atomic physics with particle and nuclear physics. Meanwhile, the entire field of AMO physics was being reshaped by advances in ultracold atom physics. Jonathan Weinstein was hired to expand in this important frontier. Jonathan uses cryogenically-cooled atoms and molecules to study cold collisions, cold chemistry, and quantum information. The most recent addition to the AMO program is Andrew Geraci. Andrew's experiments are in the rapidly growing fields of optomechanics, quantum precision sensors, and hybrid quantum systems.

# Manual for tdhf

tdhf - is a Dirac-Hartree-Fock program developed by Walter R. Johnson
Calculates energies and w.f. of valence electrons. Has Breit + QED corrections

## tdhf input

Example Fr 30 87 223 0 0 9 25 1

character*4 $ident = atomic element symbol {e.g., Fr}$jmax = # of input fields with shell orbital description (see below)
$jz = nuclear charge Z (atomic number for neutrals)$nat = atomic mass number A ( atomic weight)
$nuc = (unused set to 0)$ion = (unused set to 0)
$io = Desired relative precision = 10^(-io) - controls convergence criteria$in = index of the 1-st valence shell in the cards with orbital description (below)
$inf = (0 or 1) 0=closed-shell only if 1 do a solution for valence electron in the frozen core approximation Cards with orbital description: total number$jmax (above)
* ( n(i),kap(i),iof(i),wh(i), i = 1,jmax ) format(3i4,f12.4)
card format : n kappa iof guessed_energy_in_a.u.
* n(i): principal quantun number
* kap(i): angular quantum number kappa

if $guessed_energy >= 0.0 it is calculated internally from the hydrogenic formula The guessed_energy for valence orbitals better be good, since the program gives some dumb answers if the hydrogenic default is used.$iof governs some internal step, the mixing weight between previous and next iteration

the first $in cards describe core orbitals the rest$jz -$in are valence orbitals if$inf was 1 the next input is
$xa xalpha (some mixing parameter) read(5,*) r0,hh,mm These are grid parameters read(5,*) iparm$iparm = Type of nuclear parameters
if $iparm = 1 rnuc,cnuc,tnuc expected (all in fermis). if$iparm != 1: cnuc,anuc,b2,b4

For example for Fr the relevant input is
1.00 ! iparm
.00000 6.83430 2.30000 !rnuc,cnuc,tnuc

We mostly use $iparm = 1. Nuclear parameters can be found here (NuclearPropsWRJ.pdf) In this table tnuc=2.3 fm; rnuc=0.0000 and the relevant parameter is C(fm) read(5,*) ex$ex  affects amount of exchange in the Hartree model potential for initializing valence+frozen core potential.
Nominal value = 0

# Why is the atomic many-body problem so difficult?

One could rightfully state that the atomic-structure problem has been around for a very long time. Yes, this is true - in fact quantum mechanics has been invented to explain atomic properties. Then why do we still struggle to solve it?

Should we be embarrassed by our inability to solve this basic problem? Sure we can solve it approximately, but solving it accurately is another story.

So what is holding us back? It is the very same entanglement and complexity of Hilbert space (that is where wave functions live) that makes quantum computing so powerful. To illustrate this enormous complexity, I'll take my favorite atom, cesium. It has 55 electrons. With 3 degrees of freedom per electron (x, y, and z), the Cs wave function depends on $55 \times 3 = 155$ coordinates. As a result of the calculation I would need to store the wave function. If I  were to take a very poor grid of 10 points per coordinate, the storage would require $latex 10^{155}$ memory units.

$latex 10^{155}$ is of course an astronomically large number - in fact it exceed an estimated number of atoms in the Universe, $10^{80}$. So even if we were able to compute the Cs wave function, there is no plausible way to store it in usable form.