Atomic nucleus excited with laser: a breakthrough after many years

Physicists have been hoping for this second for a very long time: for a few years, scientists all world wide have been trying to find a really particular state of thorium atomic nuclei that guarantees revolutionary technological functions. It could possibly be used, for instance, to construct an nuclear clock that would measure time extra exactly than the perfect atomic clocks accessible immediately. It is also used to reply fully new elementary questions in physics – for instance, the query of whether or not the constants of nature are literally fixed or whether or not they change in house and time.

Now this hope has come true: the long-sought thorium transition has been discovered, its vitality is now identified precisely. For the primary time, it has been attainable to make use of a laser to switch an atomic nucleus right into a state of upper vitality after which exactly observe its return to its unique state. This makes it attainable to mix two areas of physics that beforehand had little to do with one another: classical quantum physics and nuclear physics. A vital prerequisite for this success was the event of particular thorium-containing crystals. A analysis group led by Prof. Thorsten Schumm from TU Wien (Vienna) has now printed this success along with a group from the Nationwide Metrology Institute Braunschweig (PTB) within the journal “Bodily Evaluate Letters”.

Switching quantum states

Manipulating atoms or molecules with lasers is commonplace immediately: if the wavelength of the laser is chosen precisely proper, atoms or molecules may be switched from one state to a different. On this approach, the energies of atoms or molecules may be measured very exactly. Many precision measurement methods are based mostly on this, reminiscent of immediately’s atomic clocks, but additionally chemical evaluation strategies. Lasers are additionally usually utilized in quantum computer systems to retailer info in atoms or molecules.

For a very long time, nonetheless, it appeared not possible to use these methods to atomic nuclei. “Atomic nuclei may also change between completely different quantum states. Nonetheless, it often takes far more vitality to vary an atomic nucleus from one state to a different – at the least a thousand occasions the vitality of electrons in an atom or a molecule,” says Thorsten Schumm. “For this reason usually atomic nuclei can’t be manipulated with lasers. The vitality of the photons is solely not sufficient.”

That is unlucky, as a result of atomic nuclei are literally the right quantum objects for precision measurements: They’re much smaller than atoms and molecules and are due to this fact a lot much less prone to exterior disturbances, reminiscent of electromagnetic fields. In precept, they’d due to this fact permit measurements with unprecedented accuracy.

The needle within the haystack

Because the Nineteen Seventies, there was hypothesis that there may be a particular atomic nucleus which, not like different nuclei, might maybe be manipulated with a laser, specifically thorium-229. This nucleus has two very intently adjoining vitality states – so intently adjoining {that a} laser ought to in precept be enough to vary the state of the atomic nucleus.

For a very long time, nonetheless, there was solely oblique proof of the existence of this transition. “The issue is that you need to know the vitality of the transition extraordinarily exactly so as to have the ability to induce the transition with a laser beam,” says Thorsten Schumm. “Realizing the vitality of this transition to inside one electron volt is of little use, if you need to hit the fitting vitality with a precision of 1 millionth of an electron volt in an effort to detect the transition.” It’s like in search of a needle in a haystack – or looking for a small treasure chest buried on a kilometer-long island.

The thorium crystal trick

Some analysis teams have tried to check thorium nuclei by holding them individually in place in electromagnetic traps. Nonetheless, Thorsten Schumm and his group selected a very completely different method. “We developed crystals during which giant numbers of thorium atoms are included,” explains Fabian Schaden, who developed the crystals in Vienna and measured them along with the PTB group. “Though that is technically fairly advanced, it has the benefit that we can’t solely research particular person thorium nuclei on this approach however can hit roughly ten to the ability of seventeen thorium nuclei concurrently with the laser – about one million occasions greater than there are stars in our galaxy.” The big variety of thorium nuclei amplifies the impact, shortens the required measurement time and will increase the chance of truly discovering the vitality transition.

On November 21, 2023, the group was lastly profitable: the right vitality of the thorium transition was hit precisely, the thorium nuclei delivered a transparent sign for the primary time. The laser beam had really switched their state. After cautious examination and analysis of the information, the consequence has now been printed.

“For us, it is a dream coming true,” says Thorsten Schumm. Since 2009, Schumm had centered his analysis solely on the seek for the thorium transition. His group in addition to competing groups from everywhere in the world have repeatedly achieved vital partial successes in recent times. “In fact we’re delighted that we at the moment are those who can current the essential breakthrough: The primary focused laser excitation of an atomic nucleus,” says Schumm.

The dream of the atomic nucleus clock

This marks the beginning of a brand new thrilling period of analysis: now that the group is aware of the right way to excite the thorium state, this expertise can be utilized for precision measurements. “From the very starting, constructing an atomic clock was an vital long-term purpose,” says Thorsten Schumm. “Much like how a pendulum clock makes use of the swinging of the pendulum as a timer, the oscillation of the sunshine that excites the thorium transition could possibly be used as a timer for a brand new sort of clock that will be considerably extra correct than the perfect atomic clocks accessible immediately.”

However it isn’t simply time that could possibly be measured far more exactly on this approach than earlier than. For instance, the Earth’s gravitational area could possibly be analyzed so exactly that it might present indications of mineral sources or earthquakes. The measurement technique is also used to resolve elementary mysteries of physics: Are the constants of nature actually fixed? Or can tiny modifications maybe be measured over time? “Our measuring technique is just the start,” says Thorsten Schumm. “We can’t but predict what outcomes we are going to obtain with it. It can definitely be very thrilling.”