Quantum computers rely on fundamentally different principles to today’s computers, in which each bit represents either a zero or a one. In quantum computing, each bit can be both a zero and a one simultaneously. So while three conventional bits can represent any of eight values (2^3), three qubits, as they’re called, can represent all eight values at once. That means calculations can theoretically be performed at much higher speeds.
The scientists placed two diamonds on opposite sides of the Delft University campus, 1.3 kilometers apart.
Each diamond contained a tiny trap for single electrons, which have a magnetic property called a “spin.” Pulses of microwave and laser energy are then used to entangle and measure the “spin” of the electrons.
A potential weakness of the experiment, he suggested, is that an electronic system the researchers used to add randomness to their measurement may in fact be predetermined in some subtle way that is not easily detectable, meaning that the outcome might still be predetermined as Einstein believed.
In traditional circuits, transistors are laid down in a bed of silicon that acts as an insulator to prevent crosstalk between circuits. In circuits based on quantum tunneling, silicon is replaced by nanotubes made of boron nitride and electrical pathways consisting of quantum dots—carefully placed bits of gold as small as three nanometers across (PDF).
In recent years, quantum physicists have successfully teleported entangled photons over a free-space distance of 143 kilometers (89 miles) using lasers, and 250 kilometers (155 miles) over optical fiber in the lab. In the past year we have also seen the first ground-to-air network, between a base station and an airplane flying 20 kilometers (12 miles) above. These were impressive feats, but to prove the possibility of a worldwide, satellite-based quantum network, larger distances are needed — something like the 400 kilometers (248 miles) to the ISS.
Niels Bohr is one of the greatest scientists who ever lived and a personal hero of mine. He was also a favorite of his fellow Danes when he lived in Copenhagen. Today, however, I found out just how much they loved him. Apparently, after he won the Nobel Prize in 1922, the Carlsberg brewery gave him a gift – a house located next to the brewery. And the best perk of the house? It had a direct pipeline to the brewery so that Bohr had free beer on tap whenever he wanted.
So was free beer the reason why Bohr was able to make great strides in developing quantum mechanics? Okay, probably not – but I’m sure a few late night drinking sessions with other physicists didn’t hurt.
Photons possess a number of quantum properties that can be used to encode information. You can think of photon polarization as like the rotation of a planet on its axis. In this view, the helical shape of the light wave—known as its orbital angular momentum (OAM)—is akin to the planet’s orbit around the Sun. These properties are independent of each other, and of the wavelength of light, so they can be manipulated separately. Whereas polarization occurs as a combination of two possible orientations, the OAM theoretically can have infinite values, though in practice far fewer states are available. Nevertheless, exploiting OAM greatly expands the potentially exploitable quantum states of photons we could put to use.
Quantum key distribution (QKD) uses photons polarised in two different ways to encode the 0s and 1s of an encryption key. The laws of quantum mechanics ensure the transmission is secure, as any attempt to intercept the key disturbs the polarisation – a tip-off to the receiver that the key has been seen and should be discarded.
The researchers kept the laser on track using moving mirrors both in the aircraft and on the ground. Performing the experiment shortly after sunset avoided interference from sunlight. The transmission lasted for 10 minutes, amounting to a key long enough to encrypt 10 kilobytes of data. The team presented the work at the QCrypt conference in Singapore on 12 September.
Heisenberg’s uncertainty principle, as it came to be known later, started as an assertion that when trying to measure one aspect of a particle precisely, say its position, experimenters would necessarily “blur out” the precision in its speed.
That raised the spectre of a physical world whose nature was, beyond some fundamental level, unknowable.
Photons can be prepared in pairs which are inextricably tied to one another, in a delicate quantum state called entanglement, and the weak measurement idea is to infer information about them as they pass, before and after carrying out a formal measurement.
What the team found was that the act of measuring did not appreciably “blur out” what could be known about the pairs.
UCF Professor Zenghu Chang from the Department of Physics and the College of Optics and Photonics, led the effort that generated a 67-attosecond pulse of extreme ultraviolet light. The results of his research are published online under Early Posting in the journal Optics Letters.