One of the most famous experiments in physics is the double-slit experiment, which demonstrates the wave-particle duality of light and other quantum objects. In this experiment, a beam of light passes through two narrow slits and forms a striped pattern on a screen behind them, as if the light waves interfere with each other.
But what if there were no slits in space, but only in time? This is the question that a team of physicists from Imperial College London and other institutions have explored in a new study published in Nature Physics on 3 April 2023. They have shown that a single mirror that rapidly turns on and off can create interference patterns in light waves, similar to those seen in the double-slit experiment.
The mirror they used was made of layers of gold and glass with a thin coating of indium tin oxide (ITO), a material commonly used in smartphone screens. ITO is normally transparent to infrared light, but it can become reflective when excited by another laser pulse. The researchers used this property to switch the mirror on and off by sending two ultrashort pulses of light, separated by a few tens of femtoseconds (one femtosecond is one quadrillionth of a second).
They then shone an infrared laser at the mirror and measured the waveform of the reflected light with a sensor. They found that when the mirror was turned on twice, the waveform changed from a simple, monochromatic wave to a more complex one, with different colours and shapes. This indicated that the light waves interfered with themselves as if they had passed through two slits in time.
The researchers also discovered that the ITO material could switch its optical properties much faster than previously thought possible, taking less than 10 femtoseconds to get excited. This could open new possibilities for developing devices that manipulate light at ultrafast speeds, such as optical switches, modulators and transistors.
The study is not only a remarkable demonstration of the wavelike nature of light but also a novel way of creating complex structures with light waves. The authors suggest that their technique could be used to generate other types of interference patterns, such as those seen in higher-dimensional versions of the double-slit experiment. They also speculate that their approach could be applied to other quantum objects, such as electrons or atoms, to explore their wave-particle duality in new ways.
The study is part of a growing field of research that aims to understand and control light-matter interactions at the nanoscale and beyond. Other examples include synthesizing giant molecular structures that resemble polyhedra, such as a 12-faced solid called a trick is the tetrahedron, or hijacking molecular syringes that some viruses and bacteria use to infect their hosts, and using them to deliver proteins into human cells.
These advances could lead to new applications in fields such as nanotechnology, biotechnology, quantum computing and communication. They could also shed new light on fundamental questions about the nature of matter and energy.