A NEW QUANTUM COMPUTER MODULE COMBINES PROVEN TECHNIQUES WITH ADVANCES IN HARDWARE AND SOFTWARE.
To date, many research groups have created small but functional quantum computers. By combining a handful of atoms, electrons or superconducting junctions, researchers now regularly demonstrate quantum effects and run simple quantum algorithms—small programs dedicated to solving particular problems.
But these laboratory devices are often hard-wired to run one program or limited to fixed patterns of interactions between their quantum constituents. Making a quantum computer that can run arbitrary algorithms requires the right kind of physical system and a suite of programming tools. Atomic ions, confined by fields from nearby electrodes, are among the most promising platforms for meeting these needs.
In a paper published as the cover story in Nature on August 4, researchers working with Christopher Monroe, a Fellow of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science at the University of Maryland, introduced the first fully programmable and reconfigurable quantum computer module(link is external). The new device, dubbed 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,” Monroe 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.”
The new module builds on decades of research into trapping and controlling ions. It uses standard techniques but also introduces 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.
“These are the kinds of discoveries that the NSF Physics Frontiers Centers program is intended to enable,” says 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.”
The team tested their module on small instances of three problems that quantum computers are known to solve quickly. Having the flexibility to test the module on a variety of problems is a major step forward, says Shantanu Debnath, a graduate student at JQI and the paper’s lead author. “By directly connecting any pair of qubits, we can reconfigure the system to implement any algorithm,” Debnath says. “While it’s just five qubits, we know how to apply the same technique to much larger collections.”
At the module’s heart, though, 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.
Putting the pieces together
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.
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.
o 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.
Two of the algorithms ran successfully more than 90% of the time, while the QFT topped out at a 70% success rate. The team says that this is due to residual errors in the pulse-shaped gates as well as systematic errors that accumulate over the course of the computation, neither of which appear fundamentally insurmountable. They note that the QFT algorithm requires all possible two-qubit gates and should be among the most complicated quantum calculations.
The team believes 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.
Although the module has only five qubits, its flexibility allows for programming quantum algorithms that have never been run before, Debnath says. The researchers are now looking to run algorithms on a module with more qubits, including the demonstration of quantum error correction routines as part of a project funded by the Intelligence Advanced Research Projects Activity.
RMIT researchers trialling a quantum processor capable of routing information from different locations have found a pathway towards the quantum data bus
RMIT University researchers have trialled a quantum processor capable of routing quantum information from different locations in a critical breakthrough for quantum computing.
The work opens a pathway towards the “quantum data bus”, a vital component of future quantum technologies.
The research team from the Quantum Photonics Laboratory at RMIT in Melbourne, Australia, the Institute for Photonics and Nanotechnologies of the CNR in Italy and the South University of Science and Technology of China, have demonstrated for the first time the perfect state transfer of an entangled quantum bit (qubit) on an integrated photonic device.
Quantum Photonics Laboratory Director Dr Alberto Peruzzo said after more than a decade of global research in the specialised area, the RMIT results were highly anticipated.
“The perfect state transfer has emerged as a promising technique for data routing in large-scale quantum computers,” Peruzzo said.
“The last 10 years has seen a wealth of theoretical proposals but until now it has never been experimentally realised.
“Our device uses highly optimised quantum tunnelling to relocate qubits between distant sites.
“It’s a breakthrough that has the potential to open up quantum computing in the near future.”
The difference between standard computing and quantum computing is comparable to solving problems over an eternity compared to a short time.
“Quantum computers promise to solve vital tasks that are currently unmanageable on today’s standard computers and the need to delve deeper in this area has motivated a worldwide scientific and engineering effort to develop quantum technologies,” Peruzzo said.
“It could make the critical difference for discovering new drugs, developing a perfectly secure quantum Internet and even improving facial recognition.”
Peruzzo said a key requirement for any information technology, along with processors and memories, is the ability to relocate data between locations.
Full scale quantum computers will contain millions, if not billions, of quantum bits (qubits) all interconnected, to achieve computational power undreamed of today.
While today’s microprocessors use data buses that route single bits of information, transferring quantum information is a far greater challenge due to the intrinsic fragility of quantum states.
“Great progress has been made in the past decade, increasing the power and complexity of quantum processors,” Peruzzo said.
Robert Chapman, an RMIT PhD student working on the experiment, said the protocol they developed could be implemented in large scale quantum computing architectures, where interconnection between qubits will be essential.
“We experimentally relocate qubits, encoded in single particles of light, between distant locations,” Chapman said.
“During the protocol, the fragile quantum state is maintained and, critically, entanglement is preserved, which is key for quantum computing.”
A novel solution has been identified that will make the production of special class of photons faster and easier In the age of high-speed computing, the photon is king.
Thanks to the work by a team of engineers led by Professor Amr Helmy of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering, a novel solution has been identified that will make the production of special class of photons faster and easier.
To enable these technologies to work, a photon – the smallest unit of energy – has to be tightly coupled with another photon.
Ultimately, the entire production of the photons could be completed using a single chip.
A team of physicists at the University of Toronto (U of T) have taken a step toward making the essential building block of quantum computers out of pure light.
Their advance, described in a paper published this week in Nature Physics, has to do with a specific part of computer circuitry known as a “logic gate.”
Logic gates perform operations on input data to create new outputs. In classical computers, logic gates take the form of diodes or transistors. But quantum computer components are made from individual atoms and subatomic particles. Information processing happens when the particles interact with one another according to the strange laws of quantum physics.
Light particles – known as “photons” – have many advantages in quantum computing, but it is notoriously difficult to get them to interact with one another in useful ways. This experiment demonstrates how to create such interactions.
Using a computer game, a research group at Aarhus University has found a way to gain deeper insight into the human thought process.
The results have amazed the research director, who has discovered a kind of ‘atlas of thoughts’. And that is not all. The group can also reveal which gender is best at solving quantum problems.
Are humans born with the ability to solve problems or is it something we learn along the way? A research group at the Department of Physics and Astronomy, Aarhus University, is working to find answers to this question.
The research group has developed a computer game called Quantum Moves, which has been played 400,000 times by ordinary people. This has provided unique and deep insight into the human brain’s ability to solve problems. The game involves moving atoms around on the screen and scoring points by finding the best way to do so.
In this way, ordinary people contribute to quantum physics research. Associate Professor Jacob Sherson, director of the research group, explains that a player’s ability to make a strategy and solve a problem is markedly different from the way a computer works. Based on 400,000 game solutions, he can make a start on compiling the results.