## Quantum Computers

Researchers have developed a new quantum computer module, which is the first method allowing fully programmable and reconfigurable quantum bits. The qubits are dynamically connected from the outside with patterns of laser beams, any algorithm can be run through software without modifying the base hardware.

In a paper published recently in the journal Nature, researchers show how they have introduced the first fully programmable and reconfigurable quantum computer module. The new device, called a module because of its potential to connect with copies of itself, takes advantage of the unique properties offered by trapped ions to run any algorithm on five quantum bits, or qubits—the fundamental unit of information in a quantum computer.

“For any computer to be useful, the user should not be required to know what’s inside,” Christopher Monroe, a Fellow of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science at the University of Maryland says. “Very few people care what their iPhone is actually doing at the physical level. Our experiment brings high-quality quantum bits up to a higher level of functionality by allowing them to be programmed and reconfigured in software.”

"This work is at the frontier of quantum computing, and it’s helping to lay a foundation and bring practical quantum computing closer to being a reality."

So far, other researchers have created small and functional quantum computers, by combining a small number of atoms, electrons or superconducting junctions. This work has demonstrated quantum effects and run simple quantum algorithms—small programs dedicated to solving discrete problems.Such quantum devices are often hard-wired to run one program or limited to fixed patterns of interactions between their quantum components. Making a quantum computer that can run arbitrary algorithms requires the right kind of physical system and a specific set of programming tools. Atomic ions, confined by fields from nearby electrodes, are among the most promising platforms for meeting these needs.

The new quantum computer module builds on decades of research into trapping and controlling ions. Using standard techniques but also introducing novel methods for control and measurement. This includes manipulating many ions at once using an array of tightly-focused laser beams, as well as dedicated detection channels that watch for the glow of each ion.

The scientists tested their module on small instances of three well established quantum computer problems. With the flexibility to test the module on a variety of problems, Shantanu Debnath, a graduate student at JQI and the paper’s lead author says, “By directly connecting any pair of qubits, we can reconfigure the system to implement any algorithm. While it’s just five qubits, we know how to apply the same technique to much larger collections.”

Key to the module working, is something that’s not even quantum: A database stores the best shapes for the laser pulses that drive quantum logic gates, the building blocks of quantum algorithms. Those shapes are calculated ahead of time using a regular computer, and the module uses software to translate an algorithm into the pulses in the database.

Every quantum algorithm consists of three basic ingredients. First, the qubits are prepared in a particular state; second, they undergo a sequence of quantum logic gates; and last, a quantum measurement extracts the algorithm’s output.

Related articles

The module performs these tasks using different colors of laser light. One color prepares the ions using a technique called optical pumping, in which each qubit is illuminated until it sits in the proper quantum energy state. The same laser helps read out the quantum state of each atomic ion at the end of the process. In between, a separate laser strikes the ions to drive quantum logic gates.These gates are like the switches and transistors that power ordinary computers. Here, lasers push on the ions and couple their internal qubit information to their motion, allowing any two ions in the module to interact via their strong electrical repulsion. Two ions from across the chain notice each other through this electrical interaction, just as raising and releasing one ball in a Newton’s cradle transfers energy to the other side.

To test the module, the team ran three different quantum algorithms, including a demonstration of a Quantum Fourier Transform (QFT), which finds how often a given mathematical function repeats. It is a key piece in Shor’s quantum factoring algorithm, which would break some of the most widely-used security standards on the internet if run on a big enough quantum computer.

The researchers think that eventually more qubits—perhaps as many as 100—could be added to their quantum computer module. It is also possible to link separate modules together, either by physically moving the ions or by using photons to carry information between them.

According to Jean Cottam Allen, a program director in the National Science Foundation’s physics division. “This work is at the frontier of quantum computing, and it’s helping to lay a foundation and bring practical quantum computing closer to being a reality.”

## 0 comments:

## Post a Comment