One of the largest news astounding people at the 2014 New Year is the revelation of Snowden, who released that the NSA is racing to build quantumcomputers, which could break nearly every kind of encryption. Quantum computer becomes a public hotspot overnight.
Like traditional computers, quantum computes need to be initialized, that is to say to present all qubits, the calculating units, into ground-state—its lowestenergy state. But to degenerate all the qubits to ground-state is far from being easy. Thankfully, with joint efforts of experimental scientists from
University of Science and Technology of China(USTC) and theorists from America, a universal pseudo-cooling method that can be applied to any physical system that can be simulated by a quantum computer is developed. It provides a potential way for initialization of quantum computers.
You may be confused by the name "Demon-like algorithmic quantum cooling". According to the fundamentallawsofthermodynamics, it is impossible to divide a enclosed vessel with even temperature into two parts, one part with lower the other part with higher temperature. In the 19thcentury, however, Maxwell raised an assumption to violate the Second Law of Thermodynamics. A container of gas molecules at equilibrium is divided into two parts by an insulated wall, with a door that can be opened and closed by what came to be called "Maxwell's demon". The demon opens the door to allow only the faster than average molecules to flow through to a favored side of the chamber, and only the slower than average molecules to the other side, causing the favored side to gradually heat up while the other side cools down, thus decreasing entropy.This is the well-known Maxwell's demon.
However, each quantum system has slow movement and no interference with each other even when the temperature is close to absolute zero. Nevertheless, a single quantum system still has various energy states under this circumstance. The cold components with ground-state which are needed in the initialization of quantum computer and hot components with excited state mix together. In order to realize the initialization of quantum computer, a universal pseudo-cooling method which can distil and eliminate hot components of quantum states has been proposed by the international cooperation team of USTC. "They present a novel method achieving cooling like a quantum Maxwell's demon", the reviewer appreciates their work highly.Compared to other methods which have their own emphasis on application, the proposed demon-like algorithmic quantum cooling has a universal application.
The picture shows the process of demon-like algorithmic quantum cooling. Maxwell's demon throws the hot components of quantum states out of the door and leaves behind the cold components of quantum states./ Coutesy by LI's group.
Like many other frontier science achievements, the novel method is generated from international cooperation. "Although there were some people in the team we have never meet with,"
LI Chuangfeng says,"we had a heated communication in e-mails. Even the paper title was voted from three alternative offers through e-mail. "
The submission of paper also had many stories. The algorithm design was completed in 2011 and was put on the arXiv preprint library after long discussion with reviewer in 2012. It got the final approval of release in 2014. When reviewer put forward questions about details such as the universality of the theory, the replies from joint first authors, Dr
XU Jingshi and Dr Yung Manhong, often reached 30 papers long. And there were four or five rounds of correspondence like this.
(USTC news center, FAN Qiong, TIAN Lin, YANG Yating)
