A ratchet is an asymmetric periodic structure with the possibility to extract net particle flow from unbiased driving. A classical example of a ratchet is the windmill.? In our work we focus on quantum ratchets,? with the aim of describing the interplay among quantum fluctuations, unbiased driving, and spatial potential asymmetry.??

The windmill: a classical ratchet
See some key publications:
Quantum Dissipative Ratchets
 Milena?Grifoni
 In: Nonlinear Dynamics of Nanosystems, Wiley-VCH, Weinheim (2010)
Charge ratchet from spin flip: space-time symmetry paradox
 Sergey?Smirnov, Dario?Bercioux, Milena?Grifoni und Klaus?Richter
 Phys. Rev. B?80, 201310(R) (2009)
Interplay between quantum dissipation and an in-plane magnetic field in the spin ratchet effect
 Sergey?Smirnov, D?Bercioux, Milena?Grifoni und Klaus?Richter
 Phys. Rev. B?78, 245323 (2008)
Quantum dissipative Rashba spin ratchets
 Sergey?Smirnov, Dario?Bercioux, Milena?Grifoni und Klaus?Richter
 Phys. Rev. Lett.?100, 230601-1 (2008)
Bloch's theory in periodic structures with Rashba's spin-orbit interaction
 Sergey?Smirnov, D.?Bercioux und Milena?Grifoni
 Europhys. Lett.?80, 27003 (2007)
Quantum Brownian motion in ratchet potentials: duality relation and its consequences
 J.?Peguiron und Milena?Grifoni
 Chem. Phys.?322, 169-186 (2006)
Duality relation for quantum ratchets
 J.?Peguiron und Milena?Grifoni
 Phys. Rev. E?71, 010101 (2005)
Quantum Ratchet Effect for Vortices
 J. B.?Majer, J.?Peguiron, Milena?Grifoni, M.?Tusveld und J. E.?Mooij
 Phys. Rev. Lett.?90, 056802 (2003)
Quantum Ratchets with Few Bands below the Barrier
 Milena?Grifoni, M. S.?Ferreira, J.?Peguiron und J. B.?Majer
 Phys. Rev. Lett.?89, 146801 (2002)
Duality relation for quantum ratchets
 J. Peguiron and M. Grifoni
 Phys. Rev. E? 71, 010101 (2005)
Quantum Ratchet Effect for Vortices
 J. Majer, J. Peguiron, M. Grifoni, M. Tusveld and J. Mooij
 Phys. Rev. Lett. 90, 056802 (2003)
 
 Quantum Ratchets with Few Bands below the Barrier
 M. Grifoni, M. Ferreira, J. Peguiron and J. Majer
 Phys. Rev. Lett.? 89, 146801 (2002)
 
 Nonadiabatic quantum brownian rectifiers
 I. Goychuk, M. Grifoni and P. H?nggi
 Phys. Rev. Lett. 81, 649 (1998)
Quantum ratchets
 P. Reimann, M. Grifoni and P. H?nggi
 Phys. Rev. Lett. 79, 10 (1997)