One of the areas of current research
is in using lasers to manipulate and probe entangled states of
trapped cadmium and ytterbium ion qubits, relying on the mutual Coulomb
repulsion between ions. Qubits are stored in particular
hyperfine states of the Cd+ or Yb+ ground state, and multiple
qubits are coupled through their mutual Coulomb repulsion in the
trap, mediated by appropriate external laser fields.
Implementing these types of entangling quantum logic gates requires exquisite control
of the motional state of the ions, including the laser cooling of
ions to near the ground state of motion. Worldwide heating measurements of trapped ions.
Recent highlights in this
project include:
Laser cooling to the ground state of motion for multiple ions,
and the characterization of motional heating from the ground state
in 100-200 micron trap structures.
Many groups have measured
heating of trapped ion motion, in terms of the rate dn/dt of
vibrational quanta added to the system. Below is a record of
all known measurements in traps with motional frequencies between
0.6-6.0 MHz. (If you have a new measurement, please send it to us
to be included.)
Assuming that this
heating stems for a noisy resonant electric field, we can infer the
electric field noise spectral density SE(w)
[units: (V/m)2/Hz], removing the dependence on the atomic
ion mass and the trap frequency:
Below is a history of
inferred electric field noise scaled from from the above heating measurements in
0.6-6.0 MHz
traps, as a function of the distance d to nearest electrode.
A simple model of thermal heating (Johnson noise) predicts a 1/d2 scaling (or 1/d3 scaling when the skin depth of the
electrode material is large compared to d). For fluctuating
"patch" potentials of size << d, a 1/d4 scaling is
expected. See Turchette, et al., and Deslauriers, et al. for a more detailed discussion.
Future measurement will hopefully fill the lower left corner of this
plot!
One of the areas of current research
is in using lasers to manipulate and probe entangled states of
trapped cadmium and ytterbium ion qubits, relying on the mutual Coulomb
repulsion between ions. Qubits are stored in particular
hyperfine states of the Cd+ or Yb+ ground state, and multiple
qubits are coupled through their mutual Coulomb repulsion in the
trap, mediated by appropriate external laser fields.
Implementing these types of entangling quantum logic gates requires exquisite control
of the motional state of the ions, including the laser cooling of
ions to near the ground state of motion. 
se noise from optical and
magnetic fields.
