Optical lattices H´ el` ene Perrin Laboratoire de physique des lasers, CNRS-Universit´ e Paris 13 Sorbonne Paris Cit´ e Exploring new quantum gases Les Houches, September 14–25, 2015 H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Principle of optical lattices Standing waves along 1, 2 or 3 axes, with different frequencies. 2 standing waves: 2D lattice of tubes 3 standing waves: 3D lattice I. Bloch, Nat. Phys. (2005) H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 0 �� ���� ������ �� [ ���� ] �� Comparison with free particle �� (left) of harmonic approximation �� (right) �� � � - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = E rec V 0 = E rec �� ��� ���� ������ �� [ ���� ] ���� ������ �� [ ���� ] �� ��� �� ��� �� ��� �� ��� � ��� � ��� - ��� - ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ����� - �������� � [ � ] ����� - �������� � [ � ] gray zone: potential depth V 0 zoom around q = 1: gap opening H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 2 E rec �� ���� ������ �� [ ���� ] �� �� �� �� � � - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 4 E rec V 0 = 4 E rec �� �� ���� ������ �� [ ���� ] �� ���� ������ �� [ ���� ] �� �� �� �� �� �� �� � � � � - ��� - ��� ��� ��� ��� - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 8 E rec V 0 = 8 E rec �� �� ���� ������ �� [ ���� ] �� ���� ������ �� [ ���� ] �� �� �� �� �� �� �� � � � � - ��� - ��� ��� ��� ��� - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 16 E rec V 0 = 16 E rec �� �� ���� ������ �� [ ���� ] �� ���� ������ �� [ ���� ] �� �� �� �� �� �� �� � � � � - ��� - ��� ��� ��� ��� - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 25 E rec �� ���� ������ �� [ ���� ] �� �� �� �� � � - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band structure V 0 = 32 E rec �� ���� ������ �� [ ���� ] �� �� �� �� � � - ��� - ��� ��� ��� ��� ����� - �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Bloch functions Bloch functions resemble plane waves at low V 0 , and series of peaks at large V 0 . � = �� � = � ��� V0 = 0 ��� V0 = 2 ��� [ ��� ] lowest band V0 = 4 V 0 = ��� V0 = 8 0 . . . 32 E rec V0 = 16 ��� V0 = 32 ��� - ��� - ��� - ��� ��� ��� ��� ��� �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Bloch functions Bloch functions resemble plane waves at low V 0 , and series of peaks at large V 0 . � = �� � = � � V0 = 0 � first excited V0 = 2 ��� [ ��� ] band V0 = 4 � V0 = 8 V 0 = V0 = 16 0 . . . 32 E rec - � V0 = 32 - � - ��� - ��� - ��� ��� ��� ��� ��� �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Momentum comb: sudden release Sudden release of the optical lattice: the momentum distribution presents a periodicity 2 � k . Expansion with time bosons in a 3D lattice Observation along two orthogonal 2 ms 6 ms 10 ms 14 ms 18 ms axes ⇒ recover the 3D distribution Interference between the wells From Markus Greiner’s PhD thesis. H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Band mapping: adiabatic release bosons in a 2D lattice Example: population in 2 bands (Greiner et al. 2001) V 0 = 4 E rec 10 10 5 5 0 0 ⇔ n = 0 only 10 several bands q/k − 1 0 1 5 0 q/k fermions in a 3D lattice describe − 3 − 2 − 1 0 1 2 3 (K¨ ohl et al. 2004) → 0 V 0 − noninteracting ~ − 3 − 2 − 1 0 1 2 3 10 5 noninteracting p/ ( ~ k ) 0 − 3 − 2 − 1 0 1 2 3 H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Wannier functions Wannier functions are located around a given lattice site. � = �� � � = � � = �� � � = � � = �� � � = � ��� ��� ��� � � = � � ��� � � = � � ��� � � = � � ��� ��� ��� ��� � ��� ( � ) � ��� ( � ) � ��� ( � ) ��� ��� ��� ��� ��� ��� - � - � - � � � � � - � - � - � � � � � - � - � - � � � � � �������� � [ � ] �������� � [ � ] �������� � [ � ] � = �� � � = � � = �� � � = � � = �� � � = � ��� ��� ��� � � = � � ��� � � = � � ��� � � = �� � ��� ��� ��� ��� � ��� ( � ) � ��� ( � ) � ��� ( � ) ��� ��� ��� ��� ��� ��� - � - � - � � � � � - � - � - � � � � � - � - � - � � � � � �������� � [ � ] �������� � [ � ] �������� � [ � ] H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Mott transition Observation of the Mott insulator to superfluid transition (2002): A competition between kinetic energy and interactions Small V 0 / E rec (small U / J ) Greiner et al., Nature 2002 Large V 0 / E rec (large U / J ) H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
Mott transition Mott shells in a lattice + harmonic trap (Greiner/Bloch 2011) (a) (b) SF SF 3.0 MI (n=1) MI n=3 (n=1) SF SF µ /U 2.0 MI (n=2) n=2 MI (n=1) SF 1.0 MI (n=1) n=1 x y J/U H´ el` ene Perrin, LPL – Les Houches 2015 Optical lattices
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