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To introduce quantum networks into the marketplace, engineers must overcome the fragility of entangled states in a fiber cable and ensure the efficiency of signal delivery. Now, scientists at Qunnect Inc. in Brooklyn, New York, have taken a large step forward by operating just such a network under the streets of New York City.

My new article, “Quantum Entanglement of Optical Photons: The First Experiment, 1964–67,” is intended to convey the spirit of a small research project that reaches into uncharted territory. The article breaks with tradition, as it offers a first-person account of the strategy and challenges of the experiment, as well as an interpretation of the final result and its significance. In this guest editorial, I will introduce the subject and also attempt to illuminate the question “What is a paradox?”

Some of these problems are as simple as factoring a large number into primes. Others are among the most important facing Earth today, like quickly modeling complex molecules for drugs to treat emerging diseases, and developing more efficient materials for carbon capture or batteries.

However, in the next decade, we expect a new form of supercomputing to emerge unlike anything prior. Not only could it potentially tackle these problems, but we hope it’ll do so with a fraction of the cost, footprint, time, and energy. This new supercomputing paradigm will incorporate an entirely new computing architecture, one that mirrors the strange behavior of matter at the atomic level—quantum computing.

For decades, quantum computers have struggled to reach commercial viability. The quantum behaviors that power these computers are extremely sensitive to environmental noise, and difficult to scale to large enough machines to do useful calculations. But several key advances have been made in the last decade, with improvements in hardware as well as theoretical advances in how to handle noise. These advances have allowed quantum computers to finally reach a performance level where their classical counterparts are struggling to keep up, at least for some specific calculations.

The most recent email you sent was likely encrypted using a tried-and-true method that relies on the idea that even the fastest computer would be unable to efficiently break a gigantic number into factors.

Quantum computers, on the other hand, promise to rapidly crack complex cryptographic systems that a classical computer might never be able to unravel. This promise is based on a quantum factoring proposed in 1994 by Peter Shor, who is now a professor at MIT.

But while researchers have taken great strides in the last 30 years, scientists have yet to build a quantum computer powerful enough to run Shor’s algorithm.

The next step, says Esat, is to increase the new device’s magnetic field sensitivity by implementing more advanced sensing protocols based on pulsed electron spin resonance schemes and by finding molecules with longer spin decoherence times. “We hope to increase the sensitivity by a factor of about 1,000, which would allow us to detect nuclear spins at the atomic scale,” he says.

A holy grail for quantum sensing

The new atomic-scale quantum magnetic field sensor should also make it possible to resolve spins in certain emerging two-dimensional quantum materials. These materials are predicted to have many complex magnetic orders, but they cannot be measured with existing instruments, Heinrich and his QNS colleague Yujeong Bae note. Another possibility would be to use the sensor to study so-called encapsulated spin systems such as endohedral-fullerenes, which comprise a magnetic core surrounded by an inert carbon cage.