麻豆淫院

(麻豆淫院Org.com) -- It is a truth universally acknowledged that quantum computing must have entanglement.

鈥淓ntanglement,鈥� Andrew White tells 麻豆淫院Org.com, 鈥渋s normally considered a non-negotiable part of quantum information processing. In fact, if you told me a couple of years ago that you could do quantum computing without entanglement, I would have been pretty skeptical 鈥� to say the least!鈥�

White says that he first heard the idea of non-entanglement quantum computing from Carl Caves. 鈥淚 was intrigued when Professor Caves, on sabbatical here in Australia from New Mexico, mentioned that there were sober predictions that entanglement wasn鈥檛 always necessary.鈥�

White leads a team of young experimental scientists at the University of Queensland in Brisbane, Australia. Ben Lanyon, Marco Barbieri, Marcelo Almeida and White have been studying deterministic quantum computing with only one pure qubit (DQC1). 鈥淓ntanglement is not the final story on what makes quantum information processing powerful,鈥� White insists. The Australian team鈥檚 results can be found in 麻豆淫院ical Review Letters: 鈥淓xperimental Quantum Computing without Entanglement.鈥�

鈥淣ormally, in order for quantum computing to work,鈥� White explains, 鈥渨e need to encode the information into quantum bits鈥攓ubits鈥攚hich are in a noise-free pure state. It鈥檚 known that the entanglement between these is what makes standard quantum computing powerful.鈥� He continues, 鈥淲ith a DQC1 scheme, you only have to have one pure qubit, and the rest can be noisy or mixed.鈥� The idea behind quantum information processing using entanglement is that noiselessness has to be applied in order to provide a substantial advantage over classical computing. DQC1, though, could potentially offer a more efficient and less resource-intensive method of quantum computing, since entanglement would no longer be a necessity.

鈥淔or this demonstration,鈥� White says, 鈥渨e used the smallest possible example: a circuit with just two qubits, one pure and one mixed. We ran a phase-estimation algorithm as a small example, and found in every setting there was zero entanglement, but that most of the states couldn鈥檛 be described efficiently in a classical manner.鈥�

White points out that this is suggestive that there are other possibilities, beyond entanglement, that contribute to the power provided by quantum information processing. 鈥淲e鈥檙e still chewing through the implications,鈥� he says.

鈥淭his is not a universal panacea,鈥� White admits. 鈥淔or some problems and algorithms you just need pure qubits and entanglement, problems such as Shor鈥檚 algorithm. However, there are applications and problems where the DQC1 method will work quite well, and will be more efficient than trying to get qubits that are all pure.鈥�

With so many different architectures and schemes for quantum computing 鈥� all of them trying to create a system in which all the qubits are pure 鈥� it is rare to see a group looking to find applications for a quantum information system that makes allowances for impurity and the introduction of noise 鈥� insisting that entanglement is not necessary. 鈥淭he fact is that certain classes of problems don鈥檛 need entanglement, and they don鈥檛 need all of the purity. In some cases, all that is needed is one pure qubit and the rest could be mixed. Really, with DQC1, you don鈥檛 have to work as hard as you think you do.鈥�

We are starting to build more complicated algorithms to get an idea of where this could go. Regardless, the idea that entanglement may not be necessary for some types of quantum computing is big news.鈥�

More information: B. P. Lanyon, M. Barbieri, M. P. Almeida, and A. G. White. 鈥淓xperimental Quantum Computing without Entanglement.鈥� 麻豆淫院ical Review Letters (2008). Available online: .

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