Scalable Ion Trap Architecture for Universal Quantum Computation by Collisions

We propose a scalable ion trap architecture for universal quantum computation, which is composed of an array of ion traps with one ion confined in each trap. The neighboring traps are designed capable of merging into one single trap. The universal two-qubit $\sqrt{SWAP}$ gate is realized by direct collision of two neighboring ions in the merged trap, which induces an effective spin-spin interaction between two ions. We find that the collision-induced spin-spin interaction decreases with the third power of two ions' trapping distance. Even with a $200\ \mu m$ trapping distance between atomic ions in Paul traps, it is still possible to realize a two-qubit gate operation with speed in $0.1\ kHz$ regime. The speed can be further increased up into $0.1\ MHz$ regime using electrons with $10\ mm$ trapping distance in Penning traps.Comment: 5 pages, 1 figur

Cold and Hot Nuclear Matter Effects on Charmonium Production in p+Pb Collisions at LHC Energy

We study cold and hot nuclear matter effects on charmonium production in p+Pb collisions at $\sqrt{s_\text{NN}}=5.02$ TeV in a transport approach. At the forward rapidity, the cold medium effect on all the $c\bar c$ states and the hot medium effect on the excited $c\bar c$ states only can explain well the $J/\psi$ and $\psi'$ yield and transverse momentum distribution measured by the ALICE collaboration, and we predict a significantly larger $\psi'$ $p_\text{T}$ broadening in comparison with $J/\psi$. However, we can not reproduce the $J/\psi$ and $\psi'$ data at the backward rapidity with reasonable cold and hot medium effects.Comment: 6 pages, 5 figure

Magnetic Field Effect on Charmonium Production in High Energy Nuclear Collisions

It is important to understand the strong external magnetic field generated at the very beginning of high energy nuclear collisions. We study the effect of the magnetic field on the charmonium yield and anisotropic distribution in Pb+Pb collisions at the LHC energy. The time dependent Schr\"odinger equation is employed to describe the motion of $c\bar{c}$ pairs. We compare our model prediction of non- collective anisotropic parameter $v_2$ of $J/\psi$s with CMS data at high transverse momentum. This is the first attempt to measure the magnetic field in high energy nuclear collisions.Comment: 5 pages, 4 figure