一项新的研究发表在 科学 今天, JILA 和 NIST (National Institute of St和ards 和 技术) Fellow 和 University of Colorado Boulder physics professor 你们6月 和 his research team have taken a significant step in underst和ing the intricate 和 collective light-atom interactions within atomic clocks, 宇宙中最精确的时钟.
使用立方晶格, the researchers measured specific energy shifts within the array of strontium-87 atoms due to dipole-dipole interactions. 原子密度高, these mHz-level frequency shifts—known as cooperative Lamb shifts—were spectroscopically studied. 这些变化 were studied spatially 和 compared with calculated values using imaging spectroscopy techniques developed in this experiment.
这些合作的羔羊轮班, named because the presence of many identical atoms in a tightly confining space modifies the electromagnetic mode structure around them, 随着时钟中原子的数量不断增加，这是一个重要因素吗.
“如果你能在这个网格中高密度地理解和控制这些相互作用, 你可以把网格做得越来越大,JILA的研究生威廉·米尔纳解释道, 论文的第二作者. “这是一种固有的可扩展技术，对提高时钟性能很重要.”
立方体中的时间
原子钟, 一直被认为是精确度的顶峰, 测量原子吸收或发射的光的频率的原理. Each tick of these clocks is governed by the oscillations of the quantum superposition of electrons within these atoms, 由探测激光的相应能量激发. 激光激发原子进入一种称为时钟态的量子态.
而更传统的光学晶格钟使用一维光学晶格, 只沿一个强约束方向抑制原子的运动, the strontium quantum gas clock used in this study confined the atoms in all directions by placing them in a cubic arrangement. 而使用三维晶格是一个有吸引力的时钟几何, it also requires preparing an ultracold quantum gas of atoms 和 carefully loading them into the lattice.
“情况更加复杂, 但它有一些独特的好处，因为系统具有更多的量子特性,米尔纳阐述道.
In quantum physics, the spatial arrangement of particles critically influences their behavior. 它的均匀和平衡, the cubic lattice created a controlled environment where atomic interactions were observable 和 manipulable with unprecedented precision.
观察偶极-偶极相互作用
利用立方晶格，罗斯·哈特森(Ross Hutson, JILA最近的一位博士).D.毕业), 米尔纳, 以及叶实验室的其他研究人员, were able to facilitate 和 measure the dipole-dipole interactions between the strontium atoms. 这些变化, 它们通常很小，被忽略了, arise from collective interference between the atoms behaving as dipoles when they are prepared in a superposition of the two clock states.
Because the spatial ordering of the atoms within the cubic lattice influences the dipolar coupling, researchers could amplify or diminish the dipole interactions by manipulating the angle of the clock laser relative to the lattice. Operating at a special angle—the Bragg angle—the researchers expected strong constructive interference 和 observed a correspondingly larger frequency shift.
看看合作羔羊轮班
在晶格内发生更强的偶极-偶极相互作用, the researchers found that these interactions created local energy shifts throughout the clock system.
这些能量转移, 或合作羔羊轮班, 非常小的影响通常很难检测到吗. 当许多原子聚集在一起时, 比如在立方钟晶格中, these shifts become a collective affair 和 are revealed by the newly achieved clock measurement precision. 如果不加以控制，它们会影响原子钟的准确性.
“These [shifts were] initially proposed back in 2004 as a futuristic thing to worry about [for clock accuracy],米尔纳补充道。. “现在，当你向晶格中加入更多原子时，它们突然变得更相关了。”.”
好像测量这些变化还不够有趣似的, even more interesting was that the researchers saw that the cooperative Lamb shifts weren’t uniform across the lattice, 但根据每个原子的具体位置而变化.
This local variation is significant for clock measurement: it implies that the frequency at which atoms oscillate, 因此，时钟在滴答作响,在晶格的不同部分可能略有不同. Such spatial dependence of the cooperative Lamb shifts is an important systematic shift to underst和 as researchers strive to improve timekeeping precision.
“通过测量这些变化，并看到它们与博彩平台推荐的预测值一致, 博彩平台推荐可以把钟校准得更精确,米尔纳说。.
根据他们的测量, the team realized there was a close connection between the cooperative Lamb shifts 和 the propagation direction of the clock probe laser within the lattice. This relationship allowed them to find a specific angle where a “zero crossing” was observed 和 the sign of the frequency shift transitioned from positive to negative.
“It’s a particular quantum state that experiences zero collective Lamb shift (equal superposition of ground state 和 excited state),JILA研究生闫凌峰解释道. Playing around with the connection between the laser propagation angle with respect to the cubic lattice 和 the cooperative Lamb shifts has allowed the researchers to fine-tune the clock further to be more robust against these energy shifts.
探索其他物理
除了在立方晶格中控制和最小化这些偶极子-偶极子相互作用, the JILA researchers hope to use these interactions to explore many-body physics in their clock system.
“There's some really interesting physics going on because you have these interacting dipoles,米尔纳阐述道, “所以人, 比如罗斯·哈特森, have ideas for even potentially using these dipole-dipole interactions for spin squeezing [a type of quantum entanglement] to make even better clocks.”
这项工作得到了量子系统加速器的支持.S. Department of Energy National 量子信息科学 研究 Center; along with the National 科学 Foundation’s (NSF) Quantum Leap Challenge Institute, 以及美国国家标准与技术研究院(NIST).
由JILA科学传播者Kenna Hughes-Castleberry撰写