Unconventional fermionic pairing states in a monochromatically tilted optical lattice

We study the one-dimensional attractive fermionic Hubbard model under the influence of periodic driving with the time-dependent density matrix renormalization group method. We show that the system can be driven into an unconventional pairing state characterized by a condensate made of Cooper pairs with a finite center-of-mass momentum similar to a Fulde-Ferrell state. We obtain results both in the laboratory and the rotating reference frames demonstrating that the momentum of the condensate can be finely tuned by changing the ratio between the amplitude and the frequency of the driving. In particular, by quenching this ratio to the value corresponding to suppression of the tunneling and the Coulomb interaction strength to zero, we are able to “freeze” the condensate. We finally study the effects of different initial conditions and compare our numerical results to those obtained from a time-independent Floquet theory in the large frequency regime. Our work offers the possibility of engineering and controlling unconventional pairing states in fermionic condensates.This work was conducted at the Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division (SUFD), Basic Energy Sciences (BES), U.S. Department of Energy (DOE), under contract with UT-Battelle. A.N. acknowledges support by the Center for Nanophase Materials Sciences and by the Early Career Research program, SUFD, BES, DOE. A.E.F. acknowledges the DOE, Office of Basic Energy Sciences, for support under Grant No. DE-SC0014407. A.P. was supported by NSF DMR-1506340, ARO W911NF1410540, and AFOSR FA9550-16-1-0334. (Scientific User Facilities Division (SUFD); Basic Energy Sciences (BES); U.S. Department of Energy (DOE); UT-Battelle; Center for Nanophase Materials Sciences; Early Career Research program; SUFD; BES; DOE; DE-SC0014407 - DOE, Office of Basic Energy Sciences; NSF DMR-1506340; ARO W911NF1410540; AFOSR FA9550-16-1-0334)Published versio

Cooper-pair transport through a Hubbard chain sandwiched between two superconductors: Density matrix renormalization group calculations

We present a numerical approach to study the coherent transport of Cooper pairs through a Hubbard chain, and study the role of the contacts in achieving perfect Andreev reflection. We calculate the pair transport using the Density Matrix Renormalization Group by measuring the response of the system to quantum pair fields with complex phases on the two ends of an open system. This approach gives an effective superfluid weight which is in close agreement with the Bethe Ansatz results for the superfluid weight for closed Hubbard rings.Comment: 5 pages, 6 figure

Real time evolution using the density matrix renormalization group

We describe an extension to the density matrix renormalization group method incorporating real time evolution into the algorithm. Its application to transport problems in systems out of equilibrium and frequency dependent correlation functions is discussed and illustrated in several examples. We simulate a scattering process in a spin chain which generates a spatially non-local entangled wavefunction.Comment: 4 pages, 4 eps figures, some minor corrections in text and Eq.(3