Entanglement control via reservoir engineering in ultracold gases

在单原子水平上相干控制量子系统的能力取得了惊人的进展，有望在利用量子相关性的基础上掀起一场新的技术革命。虽然一些量子技术，如量子密码学，已经进入市场，但其他的仍处于原型的水平。这就是量子计算机和量子模拟器的情况，它们有望解决目前使用的经典计算机无法解决的计算任务。我们生活在一个信息时代，我们的社会完全由计算机和互联网塑造，并依赖于越来越快的信息处理。毫无疑问，新量子信息时代的到来将使所有现有技术的范式发生转变，从而影响我们社会和文化的各个方面。大多数量子技术都依赖于纠缠的使用。然而，复合量子系统共享的这种特殊量子相关性对系统周围环境引起的噪声非常敏感。环境的作用是诱导量子系统的信息丢失，从而破坏纠缠。因此，为了使量子技术进入市场，研究环境对量子设备的有害影响并找到保护它们免受噪音影响的方法至关重要。本项目主要研究一种通过操纵环境来控制量子器件动力学的技术。更详细地说，我们考虑一个由被困在双阱势阵列（超晶格）中的原子组成的量子寄存器。量子寄存器是量子计算机的主要组成部分之一，因此寄存器中的原子需要长时间保持纠缠态。在该模型中，我们研究了将寄存器浸泡在超冷气体中。寄存器的原子和超冷气体的原子之间的碰撞会导致纠缠的损失，并限制量子器件的功能。我们研究的主要目的是研究如何通过改变超冷气体的性质来延长寄存器中的纠缠。先前对该系统的研究表明，通过增加超冷气体原子之间的相互作用，由于系统与环境之间建立了强相关性，存储在寄存器中并因环境噪声而丢失的量子信息可以部分恢复。我们的目标是通过改变环境中原子的相互作用强度来找到延长量子寄存器寿命的最佳条件。发现这些条件将构成实尺度量子技术实现的巨大进步。事实上，我们所考虑的系统已经被证明是强相关凝聚态系统的理想量子模拟器，而量子模拟器反过来可能是理解长期开放问题（如高温超导行为）的答案。

The spectacular progress in the ability to coherently control quantum systems at the level of single atoms holds the promise of a new technological revolution based on the exploitation of quantum correlations. While some quantum technologies, such as quantum cryptography, have already reached the market, others are still at the level of prototypes. This is the case of quantum computers and quantum simulators, which promise to solve computational tasks impossible to solve with classical computers like those currently used. We live in an information age, our society is completely shaped by computers and the internet, and relies on faster and faster information processing. The advent of the new quantum information era will undoubtably make a paradigm shift in all current technologies and, hence, in all aspects of our society and culture. Most quantum technologies rely on the use of entanglement. However, this peculiar quantum correlation shared by composite quantum systems is very sensitive to noise induced by the environment surrounding the systems. The effect of the environment is to induce a loss of information about the quantum system, therefore destroying entanglement. Hence, for quantum technologies to reach the market, it is crucial to study the harmful effects of the environment on quantum devices and to find ways to protect them from noise.The present project focuses on a technique to control the dynamics of a quantum device by manipulating its environment. More in detail, we consider a quantum register made of atoms trapped in an array of double-well potentials (superlattice). A quantum register is one of the main components of a quantum computer, therefore the atoms in the register need to preserve entanglement for long time. In the model we study the register is immersed in an ultracold gas. Collisions between the atoms of the register and the atoms of the ultracold gas cause loss of entanglement and limit the functionality of the quantum device. The main goal of our research is to study how, changing the properties of the ultracold gas, we can prolong the entanglement in the register. Previous studies on this system suggest that, by increasing the interaction between the atoms of the ultracold gas, the quantum information stored in the register and lost due to environmental noise can be partially regained due to strong correlations established between the system and the environment.Our aim is to find the optimal conditions to prolong the life of the quantum register by modifying the interaction strength of the atoms of the environment. Finding these conditions will constitute a tremendous advancement in the realization of real-scale quantum technologies. Systems like the one we consider, indeed, have been proven to be ideal quantum simulators of strongly correlated condensed matter systems, and quantum simulators in turn might be the answer to understanding longstanding open questions such as the behaviour of high-temperature superconductivity.