Asymmetric transport in dissipation-driven quantum systems

Many technological applications involve transport. For example, the computer I am typing on right now is powered by the flow of electric charges in a power grid. This text will then be encoded into special pulses of light, which will be transported through an optical fiber to another computer. It will then be displayed on a screen, or maybe put on paper by a printer, both devices being also powered by the transport of electric charges. All of this so you can read these few words. Hopefully you will be doing so in a warm room, thanks to a system of pipes which will transport heat from a central heating system to the room you are into. All of this is make possible by the transport devices, from the power chord of my computer to the metal pipe bringing hot water to your radiator. In this project, we will also study the transport of current, light, information, and heat, but with two essential differences. First, we will not be looking at large pipes or cables, but microscopic systems; for instance, small electrical circuits made of lumps of superconducting materials, each the diameter of a hair. These small components are described by the laws of quantum mechanics, which are very different from the one we are used to. Currently, many different research groups and companies around the world try to assemble these elements into new form of computers, which would exploit these special properties. The second difference is how our system interacts with the environment around him. In general, we want to isolate our pipes from the outside world as much as possible: just try to heat your room with a leaking radiator, or to power your TV with a severed cable! However, in the devices we will be considering, there are cases when the system could actually transport things better when we let it interact a bit with the outside world. In our project, we will try to understand how we should open the pipe, in a controlled way, to improve its transport properties.

Many technological applications involve transport. For example, the computer I am typing on right now is powered by the flow of electric charges in a power grid. This text will then be encoded into special pulses of light, which will be transported through an optical fiber to another computer. It will then be displayed on a screen, or maybe put on paper by a printer, both devices being also powered by the transport of electric charges. All of this so you can read these few words. Hopefully you will be doing so in a warm room, thanks to a system of pipes which will transport heat from a central heating system to the room you are into. Thanks to the power chord of my computer, to the water pipes, and many other devices, transport is present everywhere. And sometimes you would wish it were present: for instance, when you are stuck in a traffic jam. In this project, we have also studied transport, but instead of looking at large pipes or cables, we considered microscopic systems; for instance, small electrical circuits made of lumps of superconducting materials, each the diameter of a hair. These small components are described by the laws of quantum mechanics, which are very different from the one we are used to. More specifically, we considered a kind of particles which called bosons. To understand what makes them special, remember once again your latest traffic jam experience. When cars are driving on a one-way lane, cars block each other; you cannot go on until the car immediately in front of you has done so. This is an example of what is called an "exclusion" process. Bosons have an opposite behavior: not only can several of them occupy the same place, but, under some conditions, they want to go even more to places where other bosons are already present. That is what you may call an "inclusion" process. We have studied a specific theoretical model (in which those bosons move by interacting with their surrounding) which put these peculiar properties to the fore. We found properties such as "bosonic traffic jams", in which particles cluster on certain places, or a fundamental quantum mechanical effect known as Bose-Einstein condensation. Those results can be used to look for new effects in Experiments, and eventually to better understand the transport of energy and information in nanostructures.