FET: Small: Collaborative Research: A Probability Correlator for All-Magnetic Probabilistic Computing: Theory and Experiment

概率计算是一种计算范式，可以比传统的数字计算更有效地解决某些问题。数字计算处理的是确定性二进制位0或1，而概率计算处理的概率位(p位)有时为0，有时为1。这与量子计算不同，量子计算处理的量子位(q位)是0和1的叠加(因此总是0和1的混合)。量子计算通常需要最多的硬件资源，数字计算最少，概率计算介于两者之间。概率计算中的大多数硬件资源都致力于生成两个或更多个p比特流之间的特定相关性。这个项目将研究和演示一个系统，该系统将极大地减少与生成关联相关的硬件负担。其结果将使概率计算比目前更有效率。该项目将教育这一领域的K-12、本科生和研究生，以增加熟练的科学家和工程师的人才库，同时推动计算领域的发展。概率计算的主要挑战之一是在概率比特流之间生成所需的相关性所需的复杂硬件。这种硬件通常由微控制器、模数转换器、移位寄存器等组成，它们消耗了大量的功率，并极大地扩展了芯片上的系统面积。在这个项目中，将研究和演示一种超紧凑和极具能效的相关器或反相关器，该相关器或反相关器可以在两个p比特流之间产生可调的反相关程度。该方法是通过两个磁性隧道结(MTJ)实现的，它们的软层非常接近，因此是偶极耦合的。位状态以MTJ的电阻状态(高或低)进行编码。一个MTJ在自旋极化电流的驱动下产生一个p比特，从而产生一个自旋传递扭矩。电流以其大小确定的概率来设置电阻状态的高或低，而另一个MTJ的比特状态由与第一个MTJ的偶极耦合来确定。极强的偶极耦合将导致完美的反相关，而极弱的偶极耦合将导致不相关。偶极耦合的影响将通过向第二MTJ施加(电力产生的)局部应变来控制，该第二MTJ调制其内部能量势垒，从而将p比特之间的反相关程度从0%调制到100%。该项目将导致对使用新兴纳米磁性物理进行下一代计算的设备的新理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Probabilistic computing is a computing paradigm that can solve certain problems more efficiently than traditional digital computing. While digital computing deals with deterministic binary bits that are either 0 or 1, probabilistic computing deals with probabilistic bits (p- bits) that are sometimes 0 and sometimes 1. This is distinct from quantum computing that deals with quantum bits (q-bits) which are a superposition of 0 and 1 (and hence a mixture of both 0 and 1 all the time). Quantum computing usually requires the most hardware resources and digital computing the least, with probabilistic computing between the two. Most of the hardware resources in probabilistic computing are devoted to generating specific correlations between two or more p-bit streams. This project will study and demonstrate a system that will greatly reduce the hardware burden associated with generating correlations. The results will make probabilistic computing much more efficient than it currently is. The project will educate K-12, undergraduate, and graduate students in this field to increase the pool of skilled scientists and engineers while advancing the field of computing.One of the major challenges in probabilistic computing is the complex hardware needed to generate required correlations between probabilistic bit streams. This hardware usually consists of microcontrollers, analog-to-digital converters, shift registers, etc., that consume significant power and vastly expand the system’s footprint on a chip. In this project, an ultra-compact and extremely energy-efficient correlator or anti-correlator will be studied and demonstrated that can generate tunable degrees of anti-correlation between two p-bit streams. The approach is implemented with two magnetic tunnel junctions (MTJs) whose soft layers are in close proximity and hence dipole-coupled. Bit states are encoded in the resistance states (high or low) of the MTJs. One MTJ generates a p-bit when driven by a spin-polarized current delivering a spin-transfer-torque. The current sets the resistance state high or low with a probability determined by its magnitude, while the bit state of the other MTJ is determined by dipole coupling with the first. Very strong dipole coupling will result in perfect anti-correlation, while very weak dipole coupling will result in no correlation. The effect of dipole coupling will be controlled by applying (electrically generated) local strain to the second MTJ, which modulates its internal energy barrier, thereby modulating the degree of anti-correlation between the p-bits from 0% to 100%. This project will result in new understanding of devices that use emerging nanomagnetic physics for the next generation of computing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.