How To Improve Superconducting, Diamond Based Quantum Computers

Two research teams have made progress in the emerging field of quantum computing. One team has figured out how to reduce the complexity of superconducting qubits, while the other has aligned the frequency of two silicon qubits pulsing light from inside of a diamond lattice.

Similar to a computer bit, Qubits are a unit of measurement. The difference is that they are programmed by altering the spin of atoms and/or particles operating under the rule-set of quantum physics.

This feature increases the informational complexity of qubits to supersede that of ordinary bits which can only encode a single state: 1 or 2 respectively. Now information can be encoded as a superposition of 1 and 2 at the same time which is the main reason why quantum computers are expected to expand processing power by several orders of magnitude.

Qubits are programmed with light. By shooting electromagnetic radiation at an entangled pair from different angles and distances you can create an array of possible superposed states. Then by “exciting” these states with more energy you “activate” the data.

Since direct observation and measurement ruins the information, scientists have to be sneaky about reading it – so they shoot microwaves in to the resonant cavity in order to see how they “bounce off” of the atom/particle. Using this method they can determine how the qubit is entangled, without collapsing the superposition.

Unfortunately this requires low noise amplifiers and separate circuitry at both cryogenic and room temperatures – making it impractical at a larger scale. Which is one of the challenges to quantum computing.

So instead scientists from the university of Wisconsin-Madison decided to simplify the process by linking up their first resonant cavity filled with bosons to a second empty resonant cavity.

When the bosons are entangled in one direction they remain “metastable” in the first cavity and if they are entangled in the opposite direction they automatically tunnel through to a ground state in the second cavity.  Two separate Josephson junctions can then read the bosons and translate data in to electrical signals.

“It’s a very simple circuit,” says McDermott. The researchers detected the qubit states with a fidelity of 92%. They are confident that, with optimization, they can get to over 99%. While other qubit technologies can also reach this fidelity, McDermott’s qubits could be easier to scale-up to create a practical quantum computer.

 

Diamond Quantum Computers

Another team from Harvard University have learned how to facilitate communication between two silicon atoms trapped inside of diamond. By shooting lasers they can en-train them to oscillate at the same electromagnetic frequency. This leads to a periodic cycling between one radiant state and one darker state, the hope being that they can eventually use subtleties in wavelength to encode information.

To perform the experiment Mikhail Lukin and colleagues from Harvard University began by replacing two carbon atoms inside of a diamond with what is called a “Silicon vacancy center”. Diamonds are a good candidate for encoding qubits because of their isolation from electrical noise and permeability to light.

By placing two Silicon Vacancy centers in an optical cavity like this you can increase their  interaction

“The two SiVs are a bit like two people in a dark room trying to send Morse code signals to each other using dim flashlights,” explains Harvard’s Ruffin Evans, “If you form a cavity by placing mirrors back-to-back on each wall, the light bounces back and forth and gives the people many more chances to see the signal.”

“The novelty of our work is that, even though the interaction between light and matter is normally very weak, we’ve still been able to create an interaction between these two silicon vacancy centres using light. The next step is to harness this interaction to create a real quantum gate.”

 

 

9/25/18 Superconducting and diamond qubits get a boost

 

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