Observing the onset of effective mass.
The response of a particle in a periodic potential to an applied force is commonly described by an effective mass, which accounts for the detailed interaction between the particle and the surrounding potential. Using a Bose-Einstein condensate of (87)Rb atoms initially in the ground band of an optical lattice, we experimentally show that the initial response of a particle to an applied force is in fact characterized by the bare mass. Subsequently, the particle response undergoes rapid oscillations and only over time scales that are long compared to those of the interband dynamics is the effective mass observed to be an appropriate description. Our results elucidate the role of the effective mass on short time scales, which is relevant for example in the interaction of few-cycle laser pulses with dielectric and semiconductor materials.
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Rockson
R
Chang
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Shreyas
S
Potnis
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Ramon
R
Ramos
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Chao
C
Zhuang
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Matin
M
Hallaji
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada and Department of Electrical Engineering, Technion, Haifa 32000, Israel.
Alex
A
Hayat
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Federico
F
Duque-Gomez
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
J E
JE
Sipe
Department of Physics and Institute of Optics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, Canada.
Aephraim M
AM
Steinberg