The famous double-slit experiment – a now classic showcase of how light and matter can behave both as waves and as particles in their “classical” physical definition –seems almost magical to many of us.
Because of this unusual feature of our physical universe, the double slit experiment has puzzled physicists for decades, suggesting the possibility of multiple universes or strange quantum events. However, it was only recently that researchers from the Vienna University of Technology (You come) found a way to fully validate this experiment, using a particular measurement method on the particle.
Background: What is the double slit experiment?
This experiment was first performed by the British mathematician Thomas Young in 1802. Experience works by firing an election beam at a screen with two vertical slits. The beam must pass either through one slit or the other, creating a specific model on the wall behind them. However, in all cases of the current experiment, electrons pass through both slits at the same time, using a property called quantum superposition. Superposition allows the quantum state of an electron to be in two places at once, adding up to a coherent state. As a researcher of Tu Wien, Stephan Sponar explains, “In the classic double-slit experiment, an interference pattern is created behind the double-slit. The particles move as a wave through both apertures at the same time, and the two partial waves then interfere with each other. In some places they reinforce each other, in others they cancel each other out.
Trying to measure where a particle might be after passing through the double slit becomes a game of statistics. These statistics depend on the interference pattern of the particle, where the loci are amplified or canceled by each other. This makes the validation of experience very limited. “Of course, this is not entirely satisfactory,” said the researcher Holger Hofman from Hiroshima University, who helped develop the theory behind the experiment. “We therefore examined how the phenomenon of two-way inference can be proven based on the detection of a single particle.” Bidirectional interference is the interference that occurs between two separate particle waves.
Analysis: Separating the Waves
To examine bidirectional interference, the researchers developed a new measurement method. In this method, the quantum wave of a neutron has been split into two waves, using a crystal. The two waves moved along individual paths where they then recombined and interfered. The researchers measured this interference. They also ‘tagged’ a specific wave by manipulating the angle of the particle, so they could track which wave was going in which direction. Through trial and error, the researchers found what angles were needed to replicate the results of the double-slit experiment.
Outlook: One step closer to solving the double slot experience
“Our measurement results support classical quantum theory,” Sponar explained. “The novelty is that we don’t have to resort to unsatisfactory statistical arguments. When measuring a single particle, our experiment shows that it must have taken two paths at the same time and quantifies the respective proportions unambiguously. This study offers more insight into the process behind the famous experiment and allows further research to advance the field of quantum physics.
Kenna Castleberry is a Debrief Writer and Science Communicator at JILA (a partnership between the University of Colorado at Boulder and NIST). It focuses on deep technology, metaverse and quantum technology. You can find more of his work on his website: https://kennacastleberry.com/