每一種粒子都有一個和它的質(zhì)量、壽命、自旋嚴(yán)格相等，而電荷卻正好相反的反粒子存在，這是狄拉克在他的正電子預(yù)言中提出來的。狄拉克方程預(yù)言了一種新的電子——正電子，從而開創(chuàng)了反原子、反物質(zhì)、反世界的研究。
1932年美國物理學(xué)家安德森在宇宙線的研究中發(fā)現(xiàn)了正電子，這是人類發(fā)現(xiàn)的第一個反粒子。1932年由美國物理學(xué)家卡爾·安德森在實驗中證實了正電子的存在。隨后又發(fā)現(xiàn)了負(fù)質(zhì)子和自旋方向相反的反中子。到目前為止，已經(jīng)發(fā)現(xiàn)了300多種基本粒子，這些基本粒子都是正反成對存在的，也就是說，任何粒子都可能存在著反粒子。由反粒子組成的物質(zhì)被稱為反物質(zhì)。正反粒子和物質(zhì)如果相遇，會發(fā)生湮滅，并全部變成能量。
這些都是大家比較熟悉的，其實，在物理學(xué)領(lǐng)域，理論上也存在一種更為奇特的粒子，就是正反粒子（非學(xué)術(shù)名），就是正反粒子共同存在的一種粒子，這是1937年意大利理論物理學(xué)家馬約拉納（Ettore Majorana）提出一種觀點，所以這種粒子叫馬約拉納粒子，物理學(xué)的語言，這種粒子叫馬約拉納費米子（Majorana fermion）是一種費米子，它的反粒子就是它本身。與此相反，狄拉克費米子（Dirac fermion）則是指反粒子與自身不同的費米子。這一概念由馬約拉納于1937年提出，他對狄拉克方程式改寫得到了馬約拉納方程式，可以描述中性自旋1/2粒子，因而滿足這一方程的粒子為自身的反粒子。
從那以后，物理學(xué)家一直試圖能捕捉到這種神秘的馬約拉納費米子，現(xiàn)在終于有了很強的證據(jù)證明這種馬約拉納費米子確實存在于超導(dǎo)材料內(nèi)，這一發(fā)現(xiàn)將幫助科學(xué)家研究新型量子計算機。來自普林斯頓大學(xué)Ali Yazdani小組的這一新發(fā)現(xiàn)昨天發(fā)表在《科學(xué)》雜志上。這一發(fā)現(xiàn)具有重要意義，將啟動新型粒子發(fā)現(xiàn)的熱潮，將來科學(xué)家會試圖發(fā)現(xiàn)非超導(dǎo)情況下的馬約拉納費米子。
Theresearch team placed a long chain of iron atoms, which are magnetic, on top ofa superconductor made of lead. Normally, magnetism disrupts superconductors,which depend on a lack of magnetic fields for their electrons to flowunimpeded. But in this case the magnetic chain turned into a special type ofsuperconductor in which electrons next to one another in the chain coordinatedtheir spins to simultaneously satisfy the requirements of magnetism andsuperconductivity. Each of these pairs can be thought of as an electron and anantielectron, with a negative and a positive charge, respectively. Thatarrangement, however, leaves one electron at each end of the chain without aneighbor to pair with, causing them to take on the properties of both electronsand antielectrons — in other words, Majorana particles.
Asopposed to particles found in a vacuum, unattached to other matter, theseMajoranas are what’s called emergent particles. They emerge from the collectiveproperties of the surrounding matter and could not exist outside thesuperconductor.
Thediscovery could have implications for searches for free Majorana particlesoutside of superconducting materials. Many physicists suspect neutrinos — verylightweight particles with the strange ability to alter their identities, orflavors — are Majorana particles, and experiments are ongoing to investigatewhether this is the case.
Thefinding could also be useful for constructing quantum computers that harnessthe laws of quantum mechanics to make calculations many times faster thanconventional computers. One of the main issues in building a quantum computeris the susceptibility of quantum properties such as entanglement (a connectionbetween two particles such that an action on one affects the other) to collapsedue to outside interference. A particle chain with Majoranas capping each endwould be somewhat immune to this danger, because damage would have to be doneto both ends simultaneously to destroy any information encoded there.
