Олон улсын судлаачдын баг лазерын гэрэл атомын түвшинд хэрхэн харилцан үйлчлэлцэхийг судалж, гэрлийн талбайн бүтцээс үүдэлтэй хазайлтыг илрүүлжээ.
Швейцарын Paul Scherrer Institute (PSI)-ийн эрдэмтэд лазерын туяаг ганц ион дээр төвлөрүүлж, гэрлийн харилцан үйлчлэлийн цэгт үүсэх өөрчлөлтийг хэмжсэн байна. Туршилтаар лазерын гэрэл хамгийн хүчтэй нөлөөлөх цэг нь туяаны голд биш, харин бага зэрэг хажуу тийш шилжиж байгааг тогтоожээ. Энэхүү үзэгдэл нь ширээний теннисний бөмбөг эргэлтийн улмаас чиглэлээ өөрчилдөг “Магнусын эффект”-тэй физик шинж чанараараа ижил төстэй болохыг Physical Review Letters сэтгүүлд нийтэлжээ.
Судлаачид кальцийн ганц ионыг цахилгаан соронзон орон бүхий ионы зайд тогтоон, мэдрэгчийн үүрэг гүйцэтгүүлэн лазерын туяаны бүтцийг нарийвчлан судалсан байна. Ингэхэд гэрлийн талбайн бүтэц нарийн төвөгтэй болох үед харилцан үйлчлэлийн цэг төвөөсөө хэдэн зуун нанометрээр хазайдаг болох нь тодорхой болжээ. Энэхүү хазайлтын хэмжээ нь лазерын гэрлийн долгионы уртаас хамаардаг бөгөөд туяаг хэрхэн төвлөрүүлснээс үл хамаардаг байна.
Амстердамын их сургуулийн эрдэмтдийн онолын түвшинд таамаглаж байсан энэхүү үзэгдлийг ийнхүү туршилтаар анх удаа баталсан нь квант компьютерын хөгжилд ач холбогдолтой юм. Квант компьютерт кюбитийг (qubit) лазераар удирдах үед энэхүү багахан хэмжээний хазайлт нь алдаа үүсгэх эрсдэлтэй ч, нөгөө талаас кюбитүүдийг хооронд нь холбох боломжийг олгож, тооцооллын нарийн төвөгтэй үйлдлийг гүйцэтгэхэд тус дөхөм болж магадгүй гэж судлаачид үзэж байна.
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Table tennis players can make a ball suddenly curve by giving it just the right spin. That motion is caused by the Magnus effect, a familiar piece of physics that also influences the flight of larger balls in sports such as soccer.
Now, an international team working at the Paul Scherrer Institute PSI has observed a related effect at the atomic scale. For the first time, researchers have experimentally demonstrated the optical Magnus effect by focusing laser light on a single ion and measuring how the light interacts with it.
Instead of causing an atom to follow a curved path, the effect shifts the location where the laser interacts most strongly with the ion. That interaction point moves slightly sideways, a finding that could matter for quantum computers that use laser light to control qubits with extreme precision. The results were published in Physical Review Letters.
A Laser’s Strongest Interaction Is Slightly Off Center
At first glance, it seems reasonable to expect that an ion would interact most strongly with a laser exactly at the beam’s brightest point. But when laser light is focused very tightly, the structure of its electromagnetic field becomes more complicated.
Because of that altered field structure, the strongest interaction does not occur exactly at the center of the beam. Instead, it appears slightly to one side. This small sideways displacement is the optical equivalent of the Magnus effect that makes a spinning table tennis ball curve through the air.
That tiny shift could become important in quantum computing. Lasers are often used to change the states of qubits with very high precision. If the optical Magnus effect is ignored, it could interfere with that control and contribute to errors.
The same effect may also be useful. “The forces it generates could be used to couple qubits to one another, enabling more complex computations,” explains first author Philip Leindecker from the PSI Center for Photon Science and the Department of Physics at ETH Zurich.
Using a Single Ion to Map Laser Light
To detect the effect, the researchers used a single calcium ion as an extremely sensitive probe. The electrically charged atom was held nearly motionless in an ion trap, which uses electromagnetic fields to keep the ion fixed in place.
Trapped ions are also widely used in quantum computing. They can function as qubits, with their quantum states manipulated using carefully controlled laser pulses.
In the experiment, the team moved the calcium ion through different parts of a tightly focused laser beam and measured how strongly it interacted with the light at each position.
“Our ion acts like a tiny sensor that we can use to feel out the structure of the laser light,” Leindecker explains. “This makes it possible to measure a shift of just a few hundred nanometers.”
The measurements uncovered another surprising feature. The size of the sideways shift depends only on the wavelength of the light and not on how tightly the laser beam is focused.
Researchers at the University of Amsterdam had predicted the optical Magnus effect theoretically several years ago. By using a trapped calcium ion as a microscopic probe, the team has now observed the effect experimentally for the first time and measured its behavior in greater detail.
