Quantum Theory and the Idea that Particles Can Be in Two Places at Once

The quantum world is a strange place. If you look at an object, it changes. If you know how fast it’s moving, you can’t know where it is. Measurements that happened in the past can seemingly be erased later. Particles are sometimes waves and can be in two places at once. Cats may be both dead and alive. These are things we say when talking about the quantum world, but is this really what is going on?

Quantum mechanics is an incredibly well-established theory. It has passed every test it’s ever been subjected to. It underlies much of the technological progress we have seen in the past century, for what would electronics be without discrete energy levels, which came to us courtesy of quantum mechanics? We have the mathematics and we know how to work it, yet even after a century of debate, we don’t know what the mathematics of quantum mechanics means.

Let’s take an example: the idea that particles can be in two places at once. We are familiar with particles that are in one place at a time – an electron, say, that hits a screen and leaves a dot. These particles make an appearance in quantum mechanics as a possible solution to the equations, as we expect.

But quantum mechanics is a linear theory, which means if particles in particular places exist, then so do sums of those particles. We call those sums “superpositions”. And what is a particle in one place plus the same particle in another place? It’s not two particles – that would be described by a product, not a sum. Could you say that if we have a sum, then that’s a particle which is in both places? Well, it’s been said many times, so arguably one can.

However, I don’t know what a superposition is, other than a piece of mathematics that we need in order to explain what we observe. We need superpositions because they give particles their wave-like properties. When we see waves interfering in watercancelling out where a crest meets a trough – this is a non-quantum effect, a “classical” effect as physicists say. But it turns out that single particles can interfere with themselves. When we send an individual particle of light, or photon, through two thin slits in a plate – a double-slit – we see, as expected, a dot on the screen behind the plate. But if we continue doing this for many photons, we see an interference pattern built up from individual dots.
The only way we can explain this pattern is that each particle is a sum – a superposition – of two paths, one going through the left slit and one through the right. So why not just say that the particle goes both ways?
Source: https://www.newscientist.com/

Nanodevice 100 Times Faster Than The Usual Transistor

Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a nanodevice that operates more than 10 times faster than today’s fastest transistors, and about 100 times faster than the transistors you have on your computers. This new device enables the generation of high-power terahertz waves. These waves, which are notoriously difficult to produce, are useful in a rich variety of applications ranging from imaging and sensing to high-speed wireless communications. The high-power picosecond operation of these device also hold immense promise to some advanced medical treatment techniques such as cancer therapy. The team’s pioneering compact source, described today in Nature, paves the way for untold new applications.

Terahertz (THz) waves fall between microwave and infrared radiation in the electromagnetic spectrum, oscillating at frequencies of between 100 billion and 30 trillion cycles per second. These waves are prized for their distinctive properties: they can penetrate paper, clothing, wood and walls, as well as detect air pollution. THz sources could revolutionize security and medical imaging systems.

What’s more, their ability to carry vast quantities of data could hold the key to faster wireless communications.

THz waves are a type of non-ionizing radiation, meaning they pose no risk to human health. The technology is already used in some airports to scan passengers and detect dangerous objects and substances.

Despite holding great promise, THz waves are not widely used because they are costly and cumbersome to generate. But new technology developed by researchers at EPFL could change all that. The team at the Power and Wide-band-gap Electronics Research Laboratory (POWERlab), led by Prof. Elison Matioli, built a nanodevice (1 nanometer = 1 millionth of a millimeter) that can generate extremely high-power signals in just a few picoseconds, or one trillionth of a second, – which produces high-power THz waves.

The technology, which can be mounted on a chip or a flexible medium, could one day be installed in smartphones and other hand-held devices. The work first-authored by Mohammad Samizadeh Nikoo, a PhD student at the POWERlab, has been published in the journal Nature.

Source: https://actu.epfl.ch/