The pulse of an atom's magnetic heart as it ticks back and forth between quantum states has been timed in a laboratory.
Physicists used a scanning tunneling microscope to observe electrons as they moved in sync with the nucleus of an atom of titanium-49, allowing them to estimate the duration of the core's magnetic beat in isolation.
"These findings," they write in their paper, "give an atomic-scale insight into the nature of nuclear spin relaxation and are relevant for the development of atomically assembled qubit platforms."
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Spin is a term physicists use to describe a quantum version of angular momentum. Not only is it fundamental to the behavior of magnets, it often forms the basis of quantum computing as a 'bit' of information, known as a qubit.
Numerous subatomic particles buzzing about in a quantum storm contribute to a nucleus's overall spin, though the flip-flop of the collective spins as they adopt a configuration is easily influenced by the atom's surroundings. Knowing the characteristics of this collective spin state before the environment messes with it could give engineers a new kind of qubit to play with.
Observing the spin state of a nucleus without affecting it poses a real dilemma, though. So a team led by physicists Evert Stolte and Jinwon Lee of the Delft University of Technology in the Netherlands thought they may be able to use the behavior of electrons in an atom as a proxy.
Several years ago, researchers determined they could use what's known as the hyperfine interaction between electrons and their nucleus as a guide, without needing to directly interfere with its magnetic dance.
"The general idea had been demonstrated a few years ago, making use of the so-called hyperfine interaction between electron and nuclear spins," explains physicist Sander Otte of the Delft University of Technology. "However, these early measurements were too slow to capture the motion of the nuclear spin over time."
To compensate for this, the researchers developed a pulsed measurement scheme, whereby a scanning tunneling microscope measures an atom with a known nuclear spin in short pulses with a break in between, rather than one continuous measurement.
They chose for their experiment a stable, naturally occurring isotope of titanium called titanium-49. This isotope is a popular choice for nuclear physics research because its nucleus has interesting magnetic-reactive properties and a strong spin that scientists can manipulate to understand the behavior of atomic nuclei.
Under their pulsed regime, Stolte and Lee observed the switching of the atom in real-time in the readout displayed on their computer screen. They determined that there was a time interval of about five seconds between each switch – a measurement that they could perform faster than the nucleus oscillated.
"We were able to show that this switching corresponds to the nuclear spin flipping from one quantum state to another, and back again," Stolte says. "The first step in any new experimental frontier is being able to measure it, and that is what we were able to do for nuclear spins at the atomic scale."
The research has been published in Nature Communications.