High-speed feedback trap based on optical tweezers

我和我的团队提议建立一个基于光镊的高速三维反馈陷阱，以研究统计物理和生物物理中的基本问题。在过去的十年中，我们已经开发出一种方法，使用反馈陷阱来定量研究被困在二维“虚势”，可以任意操纵的粒子的运动。 我们已经使用反馈陷阱来进行非平衡统计物理的基本测试，重点是将热力学与信息论联系起来的问题。 两个亮点包括对Landauer原理的测试，该原理指出，擦除一位信息不可避免地需要每位至少kT ln 2的功，以及非平衡系统熵的函数形式的首次测量。使用由2014年RTI奖资助开发的仪器，我们证明了光镊可以提供制作反馈陷阱所需的力。 我们的陷阱的最新版本已经证明了1000倍的速度相对于我们最初的设计和空间尺度减少了100倍。 我们还展示了一个基于虚拟双阱势的两态胶体系统，该系统在10 nm的空间尺度下具有近1 kHz的跃迁速率。 最后，对于简单的捕获，反馈可以将陷阱的有效刚度增加40倍，而不增加光束强度。 这项仪器工作刚刚出现在应用物理快报上，在美国物理研究所的Scilights网站上突出显示。到目前为止，主动反馈操纵已被限制在横向（xy）运动的粒子在陷阱。 在轴向（z）方向上的捕获限于由反馈镊子提供的被动捕获。 不幸的是，梁的几何形状（和辐射压力）导致轴向刚度明显低于横向刚度。 在所提出的设置中，我们将改进传感器和致动器设计，以增加垂直运动的主动控制。 进一步的改进将使总体反馈带宽增加10至1 MHz。**增加三维控制和进一步加快陷阱带宽将导致新类型的应用。 第一个目标是将随机热力学扩展到基于随机性的量，这是由于缺乏统计而在其他实验中未探索的细节水平。 第二个目标是操纵不稳定的物体，如反馈陷阱中的气泡。 第三个目标是重新优化光镊的参数，以充分利用反馈控制提供的可能性，这是迄今为止还不可能实现的壮举，因为反馈控制需要针对所有三个轴。 因此，我们建议建造的仪器将使统计物理学的新基础测试和生物物理学的新测量技术成为可能。

My group and I propose to build a high-speed, three-dimensional feedback trap based on optical tweezers, to study fundamental problems in statistical physics and biophysics. Over the past ten years, we have developed a way to use feedback traps to quantitatively study motion of particles trapped in two-dimensional "virtual potentials" that may be arbitrarily manipulated. We have used feedback traps to carry out fundamental tests of nonequilibrium statistical physics, focusing on questions connecting thermodynamics with information theory. Two highlights include a test of Landauer's principle, which states that the erasure of one bit of information inevitably requires work of at least kT ln 2 per bit and the first measurement of the functional form of nonequilibrium system entropy.******Using an instrument developed with funding from a 2014 RTI award, we showed that optical tweezers can provide the force needed to make a feedback trap. The latest version of our trap has demonstrated a speed-up of 1000 times relative to our original design and a decrease in spatial scale by a factor of 100. We have also demonstrated a two-state colloidal system based on a virtual double-well potential that had nearly 1 kHz transition rates at a spatial scale of 10 nm. Finally, for simple trapping, feedback can increase the effective stiffness of the trap by a factor of 40, with no increase in beam intensity. This instrumentation work has just appeared in Applied Physics Letters, where it was highlighted on the Scilights website of the American Institute of Physics.******To date, active feedback manipulation has been confined to lateral (xy) motions of particles in the trap. Trapping in the axial (z) direction was limited to the passive trap provided by feedback tweezers. Unfortunately, the beam geometry (and radiation pressure) leads to axial stiffnesses that are significantly lower than the lateral ones. In the proposed setup, we will improve sensor and actuator design to add active control of vertical motions, as well. Further improvements will increase the overall feedback bandwidth by 10 to 1 MHz.******Adding three-dimensional control and further speeding up the trap bandwidth will lead to qualitatively new types of applications. A first goal is to extend stochastic thermodynamics to trajectory-based quantities, a level of detail that is unexplored in other experiments for lack of statistics. A second goal is the manipulation of unstable objects such as air bubbles in a feedback trap. A third goal is to re-optimize the parameters of optical tweezers to take full advantage of the possibilities offered by feedback control, a feat that has not been possible so far, as feedback control needs to be for all three axes. The instrument that we propose to build will thus make possible new fundamental tests of statistical physics and also new measurement techniques in biophysics.*****