The cyberattack on the Hillel Yaffe Medical Center in Hadera a month ago, in which attackers demanded a large ransom that was turned down by Israel’s Health Ministry and forced staffers to return to medical records on paper, was only a hint of what could happen in the future of data security. 

Quantum computers will revolutionize our computing lives in the future.  For some critical tasks they will be incomparably faster and use much less electricity than today’s computers.  However. these computers will be able to crack most of the encryption codes currently used to protect our data, leaving vital security information vulnerable to attacks.  

At present, most computer security relies on mathematical manipulations that ensure a very high level of security; it would take a regular computer billions of years to break one of those codes.  But in our quantum future, new methods of encryption that rely on the laws of physics, rather than mathematical equations, will need to be developed.  

Quantum computers perform calculations based on the probability of an object’s state before it is measured. Classical computers carry out logical operations using the definite position of a physical state. These are usually binary, meaning its operations are based on one of two positions. A single state such as on or off, up or down, 1 or 0 is called a bit.

In quantum computing, operations instead use the quantum state of an object to produce what’s known as a qubit. These states are the undefined properties of an object before they’ve been detected, such as the spin of an electron or the polarization of a photon.

Rather than having a clear position, unmeasured quantum states occur in a mixed “superposition,” not unlike a coin spinning through the air before it lands in your hand.

These superpositions can be entangled with those of other objects, meaning their final outcomes will be mathematically related even if we don’t know yet what they are.

The complex mathematics behind these unsettled states of entangled “spinning coins” can be plugged into special algorithms to make short work of problems that would take a classical computer a long time to work out – if they could ever calculate them at all.

Such algorithms would be useful in solving complex mathematical problems, producing hard-to-break security codes, or predicting multiple particle interactions in chemical reactions.

One potential approach is to use the quantum properties of single photons (particles of light) to securely encrypt a message so that any attempt to hack it is immediately detectable by both the sender and recipient. But getting a suitable source of single photons has been an immense challenge.  

Now, a team of researchers, led by Prof. Ronen Rapaport and Dr. Hamza Abudayyeh of the Racah Institute of Physics at the Hebrew University of Jerusalem (HUJI) – together with Prof. Monika Fleischer, Annika Mildner and others at the University of Tübingen in Germany – has achieved a significant breakthrough.  Their findings bring us closer to a simple and efficient method of quantum encryption, and were published in the journal ACS Nano under the title “Overcoming the Rate-Directionality Trade-off: A Room-Temperature Ultrabright Quantum Light Source.” 

Banks and government departments are already investing heavily in quantum encryption that relies on laser beams.  However, laser beams often release several photons at once or none at all.  What is needed for optimum security is a source that can emit a fast but steady stream of single photons—in one direction and at room temperature. 

The HUJI team developed a system that uses fluorescent crystals in the form of specks so tiny that special microscopes are needed to see them.  Known as quantum dots, each one measures much less than a thousandth of the width of a human hair.  A laser beam shone at the quantum dot causes it to fluoresce and emit a stream of single photons. 

These quantum dots are individually mounted on golden pinheads – except, of course, it is a nano-pinhead, or nanocone, almost a hundred- thousandth the size of a regular pinhead. Nanocones are able to increase the quantum dot emission of photons 20-fold.  This stream of photons is then shot off in a single direction by a “Bragg grating” acting as a type of antenna.  

The HUJI-Tübingen device is useful not only for quantum encryption, but in other situations that rely on quantum bits to encode information such as quantum computation.  “At present, we have a good prototype that has the potential for commercialization in the near future,” explained Rapaport.  

The advantage of quantum cryptography lies in its physical determinism.  “Laws of science cannot be broken. A single photon cannot be split, no matter how hard one tries.  Mathematical complexities might be very difficult to solve, however they are vulnerable to attack and breaches unlike quantum-based security systems,” concluded Abudayyeh.  The researchers are currently improving their device so that it can provide an even more reliable and efficient stream of single photons that could be used in a wide range of quantum technologies.