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March 20, 2009

Quantum Computer Update: Tuneable qubits, molecular qubits, 128 qubit Chip Close to Commercial Sales

1. Multi qubit synchronization of compound Josephson junction rf-SQUIDs is discussed in a research paper. It is one of the key components of Dwave Systems adiabatic quantum computer.

In the comments, CTO Geordie Rose reveals that after - another rev (some tweaks) of the 128 qubit design, they will 95% likely be selling the 128 qubit chip and service.

It is almost certain >95% that this is going to be the design included in the first 128-qubit systems we will be selling, based on the results we are seeing from device performance on Rainier chips. That being said there will be new wafer runs with slightly modified designs (parameter variations) between now and shipping, so the actual chips we have in Vancouver now will probably not be the ones included in the sold systems. Our total focus now is on building and selling access to our technology at the 128-qubit level.


If they do start selling a 128 qubit quantum computer this will fulfill the Long Bets Prediction made in 2006

“There will be a quantum computer with over 100 qubits of processing capability sold either as a hardware system or whose use is made available as a commercial service by Dec 31, 2010”


2. Quantum computer annealing

Implementation of a Quantum Annealing Algorithm Using a Superconducting Circuit

A circuit consisting of a network of coupled compound Josephson junction rf-SQUID flux qubits has been used to implement an adiabatic quantum optimization algorithm. It is shown that detailed knowledge of the magnitude of the persistent current as a function of annealing parameters is key to implementation of the algorithm on this particular type of hardware. Experimental results contrasting two annealing protocols, one with and one without active compensation for the growth of the qubit persistent current during annealing, are presented in order to illustrate this point.







3. Researchers at the Universities of Edinburgh (Scotland) and Manchester (England) have created a molecular device they suggest could act as a building block for super-fast quantum computers.

The scientists achieved the breakthrough by combining tiny magnets with molecular machines that can shuttle between two locations without the use of external force. The manoeuvrable magnets could one day be used as the basic component in quantum computers.

Conventional computers work by storing information in the form of bits, which can represent information in binary code - either as zero or one.

Quantum computers would use quantum binary digits, or qubits, which are far more sophisticated as they are capable of representing not only zero and one, but a range of values simultaneously.

According to Professor Richard Winpenny, of the University of Manchester's School of Chemistry: "To perform computation we have to have states where the qubits speak to each other and others where they don't - rather like having light switches on and off.

"Here we have shown we can bring the qubits together, control how far apart they are, and potentially switch the device between two or more states. The remaining challenge is to learn how to do the switching, and that's what we're trying to do now."

Professor David Leigh, of Edinburgh University's school of chemistry, added: "This development brings super-fast, non-silicon based computing a step closer."


4. Tunable qubits

Mooij says that it is possible to strongly couple the qubits to a resonator. “We choose to make the qubits the same frequency of the resonator. We tune this gap of the superconducting qubit to a harmonic oscillator. The qubit communicates with the oscillator while they are at the same frequency.” After a set amount of time, it is possible to then decouple the qubit from the oscillator and tune a new qubit to the frequency. Tuning is done by means of the addition of another flux loop in order to control the energy splitting. The Netherlands group found that it is possible to do this within nanoseconds - making the process very fast.

The next step, Mooij explains, is to transfer information from the resonator to another qubit. So far, the group has only shown that gap tuning is possible with one qubit, and no transfer of information has taken place. However, it should be possible for a qubit to communicate with the resonator, and then for the resonator to communicate that information to another qubit. “Any pair of qubits can be chosen for the interaction,” he points out. “If we can do it with one, as we have demonstrated, we can do it with many. But we still have not gotten any information from the resonator, and we need to take the next step.”

Tunable qubits are applicable in a number of circumstances. Being able to control the qubits’ frequencies has practical applications in terms of quantum optics and physics, as well as for quantum gates. Being able to control qubits and their coupling is a potentially large step forward in terms of technological and scientific development.

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