From menial industrial chemistry to the forefront of theoretical physics

When Sandu Popescu completed his studies at the University of Bucharest, he didn’t have to deal with the challenge that many new graduates face today – finding a job.

Image: Anna I Popescu

The communist government of early-80s Romania had already decided that for him. They sent him to a chemical factory.

The environment was inevitably an unpleasant one in which to operate, amid the racket created by pumps the size of rooms, and the work itself wasn’t exactly stimulating.

Among the plant’s other employees was an older lady whose sole duty was to periodically chuck a bucket of aluminium salts into dirty water to clean it. Popescu’s job was to keep her awake.

He did that for three years.

Worse still, not being a member of the Communist Party meant that getting a job at the university, doing the physics he loved, was out of the question. Rather than stick it out in the factory, he took a risk and left Romania, leaving his family, friends and possessions behind, using the only legal way available at the time – definitive departure. Meaning: you leave and never come back.

That gamble paid off. He soon met Professor Yakir Aharonov, a leading expert in quantum physics and the co-discoverer, alongside David Bohm, of the Aharonov-Bohm effect, who accepted him as a PhD student at Tel Aviv University in Israel.

“I soon found myself spending long afternoons discussing free will, the flow of time and quantum physics with one of the best physicists in the world,” he says. “I couldn’t believe it was the same me, who a few months before was dressed in a dirty overall, wearing rubber boots and a hard hat, in the night shift, in a toxic place, solving clandestinely some physics problems to kill boredom, while doing nothing else than keeping an eye on the clock for when to wake up that nice lady – she did fall asleep, of course.”

Doing his PhD, Popescu regained a foothold on the path to where he is today. He’s now Professor Popescu, based at the University of Bristol for the past 16 years having come there via Cambridge and Brussels, and the winner of the IOP’s 2016 Dirac Medal for his work on fundamental aspects of quantum mechanics and for results that make him one of the fathers of quantum information. His talents have clearly been put to much greater use than back in that chemical factory: “They didn’t need me,” he acknowledges.

Nevertheless, Popescu speaks warmly of growing up in Oradea, in the west of Romania near the border with Hungary, despite the regime of the time. “Look, if it had been that bad everything would have kicked off sooner,” he says. “But, before one grows up and realises what’s really going on, all the lies and so on, it was fine. I had a very happy childhood.”

It was in high school that Popescu took an interest in physics, and as an undergraduate he became attracted by the strangeness of the field he now studies, quantum mechanics. “I thought smart people must have worked it all out already,” he says. But that was not the case.

He would begin to look for those deep answers himself. Popescu’s most notable research has been in the area of quantum nonlocality – one of those counterintuitive aspects of quantum physics far removed from our everyday experience. He explains that in classical physics, which governs our daily lives, every effect we experience happens locally: “If I want to talk to you, my mouth moves the air, that moves more air, and, eventually, air moves your eardrum. Or we send a signal down a phone line. Everything moves from one place to a neighbouring one.”

But in quantum physics that is not necessarily the case, most notoriously in the “spooky action at a distance” seen in the phenomenon of entanglement as discovered by John Bell in 1964. The instantaneous transmission of information in entanglement can remain consistent with relativity – in which signals can’t propagate faster than light – as in the quantum world nature is probabilistic: the same causes won’t produce the same effects every time.

Nonlocality was largely ignored for almost 30 years. That changed in the early 90s when a number of discoveries thrust it to the core of physics – and Popescu was instrumental in this.

In 1992, he discovered that nonlocality is an absolutely generic feature of quantum physics, inherent to almost all quantum states. Two years later, he and Daniel Rohrlich showed that even stronger nonlocality than what is allowed by quantum mechanics could exist in nature and still not violate relativity. Whether or not such stronger nonlocality exists, and, if not, why nonlocality is limited in nature, is now one of the major open questions in fundamental physics.

Along with other colleagues, Popescu then discovered entanglement concentration, dilution and purification, establishing the quantitative description of quantum nonlocality and the modern view of nonlocality as a resource.

As well as being a top theoretician, Popescu has contributed to experimental work in quantum physics: he designed the scheme that led to the first experimental demonstration of quantum teleportation – arguably one of the most iconic experiments in quantum information – and has been granted several patents to commercialise his work.

Further, he’s the discoverer, along with Aharonov and his group, of several apparent paradoxes: the quantum Cheshire cat – in which a particle and its properties can be separated, just as the feline encountered by Alice in Wonderland disappears but leaves its grin behind – and the quantum pigeonhole effect, in which, unlike pigeons, you can put three particles into two boxes and yet ensure that no two particles are found in the same box.

Getting to the bottom of this sort of thing is still what motivates Popescu – a far cry from the shut -up-and-calculate approach espoused by many physicists. And where paradoxes frustrate some, he sees learning opportunities. “I love paradoxes,” he says. “The fact that we are so often surprised, that we view so many quantum effects as paradoxical, is a clear sign that we don’t fully understand what’s going on. Rather than try to avoid paradoxes, we should seek them out and learn from them. They are the instances when we push nature to the extreme and make it reveal its true self.”

And as for his own true self, it’s plainly the guy working at the forefront of theoretical physics – not in menial industrial chemistry.

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Christopher White

Christopher White

Christopher was the IOP's Publications & Content Editor.
Christopher White

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