323,186 research outputs found
Many Body Quantum Chaos
Get PDFThis editorial remembers Shmuel Fishman, one of the founding fathers of the research field "quantum chaos", and puts into context his contributions to the scientific community with respect to the twelve papers that form the special issue
Negative Differential Conductivity in an Interacting Quantum Gas
Get PDFNegative differential conductivity (NDC) is a widely exploited mechanism in many areas of research dealing with particle and energy transport. We experimentally realize such a many body quantum transport system based on ultracold atoms in a periodic potential. We prepare our system by loading Bose condensed rubidium atoms in a 1D optical lattice with high atom occupancy per lattice site. Subsequently, we remove all the atoms from a central lattice site. While the atoms from neighboring sites tunnel into the empty site, we observe NDC in the resulting current voltage characteristics and investigate the microscopic mechanism behind it [R. Labouvie, B. Santra, S. Heun, S. Wimberger, H. Ott, arXiv:1411.5632]
Light shift induced behaviors observed in momentum-space quantum walks
Get PDFQuantum walks (QWs) have seen many advances both experimentally and theoretically over the last decade with many proposed applications. Recently, a QW was experimentally realized utilizing a Bose-Einstein Condensate (BEC) in momentum space. This QW was observed to be stable up to fifteen steps and exhibited behavior that agreed generally well with theoretical predictions. However, the QW also showed interesting behavior within the momentum distribution that wasn’t adequately explained by the theory. We propose a new theoretical model to offer an explanation based upon the parameters within the conducted experiments. This model also predicts that the discrepancy is dependent upon the initial momentum states used in creating the QW
Controlling the momentum current of an off-resonant ratchet
No full textWe experimentally investigate the phenomenon of a quantum ratchet created by exposing a Bose-Einstein condensate to short pulses of a potential which is periodic in both space and time. Such a ratchet is manifested by a directed current of particles, even though there is an absence of a net bias force. We confirm a recent theoretical prediction [M. Sadgrove and S. Wimberger, New J. Phys. 11, 083027 (2009)] that the current direction can be controlled by experimental parameters which leave the underlying symmetries of the system unchanged. We demonstrate that this behavior can be understood using a single variable containing many of the experimental parameters and thus the ratchet current is describable using a single universal scaling law
Experimental study of Spontaneous Emission in the Quantum Walk
No full textWe have recently realized a quantum walk of a Bose-Einstein Condensate (BEC) of Rubidium 87 atoms by applying a periodic kicking potential to change the momentum state of the atoms and using microwave pulses to control the internal state. This periodic potential was generated by two counter-propagating, off-resonant frequency stabilized laser beams. This setup is stable to generate a quantum walk for tens of steps, however, it is affected by spontaneous emission induced by the same laser beams used to generate the kicking potential. We have investigated this spontaneous emission by varying a few parameters including the power of the kicking laser beams. The results of this study allow us to determine the robustness of the quantum walk during the experiment. These findings can also be used in other related experiments involving the use of BECs as a basis
Quantum to Classical Walk Transitions Tuned by Spontaneous Emissions
Get PDFWe have recently realized a quantum walk in momentum space with a rubidium spinor BoseEinstein condensate by applying a periodic kicking potential as a walk operator and a resonant microwave pulse as a coin toss operator. The generated quantum walks appear to be stable for up to ten steps and then quickly transit to classical walks due to spontaneous emissions induced by laser beams of the walk operator. We investigate these quantum to classical walk transitions by introducing well-controlled spontaneous emissions with an external light source during quantum walks. Our findings demonstrate a scheme to control the robustness of the quantum walks and can also be applied to other cold atom experiments involving spontaneous emissions
Two-time correlation functions in dissipative and interacting Bose-Hubbard chains
No full textA method is presented for the systematic derivation of a hierarchy of coupled equations for the computation of two-time correlation functions of operators for open many-body quantum systems. We show how these systems of equations can be closed in mean-field and beyond approximations. Results for the specific example of the spectral weight functions are discussed. Our method allows one to access the full temporal evolution, not just the stationary solution, of non-equilibrium open quantum problems described by a Markovian master equation
Driven collective quantum tunneling of ultracold atoms in engineered optical lattices
No full textCollective quantum tunneling of a Bose-Einstein condensate between two parts of an optical lattice separated by an energy barrier is theoretically investigated. We show that by a pulsewise change of the barrier height, it is possible to switch between a tunneling regime and a self-trapped one. This property of the system is explained by effectively reducing the nonlinear dynamics of the system to that of a particle moving in a double square well potential. The analysis is performed for both attractive and repulsive interatomic forces, and emphasizes the experimental relevance of our findings
Engineering many-body quantum dynamics by disorder
No full textGoing beyond the currently investigated regimes in experiments on quantum transport of ultracold atoms in disordered potentials, we predict a crossover between regular and quantum-chaotic dynamics when varying the strength of disorder. Our spectral approach is based on the Bose-Hubbard model describing interacting atoms in deep random potentials. The predicted crossover from localized to diffusive dynamics depends on the simultaneous presence of interactions and disorder and can be verified in the laboratory by monitoring the evolution of typical experimental initial states
To the Special Issue On Workshop On Noisy Many-body Systems Preface
No full textWe give a brief sketch of the interdisciplinary field of noisy systems, classical as well as quantum ones, with great perspectives toward many-body systems and the engineering of their dynamics by the noise. A tiny cross section of the vast field is introduced along the lines of the research papers contained in this special issue
- …
