Researchers are developing quantum memory that can hold information for long periods of time - a step towards developing practical quantum computers.

Present day computers or classical computers, as they are called, uses bits to store information. A bit is the fundamental unit of information for a classical computer. It can be either On (1) or Off (0). By arranging a series of bits, information or calculations can be carried out by classical computers. This technology is what defines the present day digital age where information is processed in a series of 0s and 1s.

A quantum computer uses a different unit for storing information; a qubit. Qubits are made up of atoms and because of the laws of quantum mechanics, exhibit peculiar behaviors that can be utilized in quantum computing. Instead of storing information in 2 states, qubits can store information in three states; an up state (1), a down state (0), and a superposition state which is both up and down at the same time. This is achieved because of quantum mechanics. Atoms have a spin up stage and a spin down stage that can be interpreted as 1 and 0. But they also can achieve superposition which is both up and down.

In terms of computing power, this means that a quantum computer can theoretically perform a calculation in one step where a classical or digital computer may take several. A classical computer can be programmed to dial a million phone numbers, it will perform this by dialing a phone one million times. A quantum computer can dial the same million numbers all at the same time, in one step.

At the moment there are quantum computers that have been built but because of technological limitations, are as big as a room. And the most a quantum computer have calculated at the moment is finding the factors of the number 15. But given time, just like the massive computers in the early 50s, these will result in smaller, compact computers.

Researchers at the University of Sydney and Dartmouth College have developed a new way to design quantum memory, bringing quantum computers a step closer to reality. The results will appear June 19 in the journal Nature Communications.

Quantum computing may revolutionize information processing, by providing a means to solve problems too complex for traditional computers, with applications in code breaking, materials science and physics. But figuring out how to engineer such a machine, including vital subsystems like quantum memory, remains elusive.

In the worldwide drive to build a useful quantum computer, the simple-sounding task of effectively preserving quantum information in a quantum memory is a major challenge. The same physics that makes quantum computers potentially powerful also makes them likely to experience errors, even when quantum information is just being stored idly in memory. Keeping quantum information "alive" for long periods, while remaining accessible to the computer, is a key problem.

The Sydney-Dartmouth team's results demonstrate a path to what is considered a holy grail in the research community: storing quantum states with high fidelity for exceptionally long times, even hours according to their calculations. Today, most quantum states survive for tiny fractions of a second.

Video: Quantum Computers vs Classical Computers

"Our new approach allows us to simultaneously achieve very low error rates and very long storage times," said co-senior author Dr. Michael J. Biercuk, director of the Quantum Control Laboratory in the University of Sydney's School of Physics and ARC Centre for Engineered Quantum Systems. "But our work also addresses a vital practical issue – providing small access latencies, enabling on-demand retrieval with only a short time lag to extract stored information."

The team's new method is based on techniques to build in error resilience at the level of the quantum memory hardware, said Dartmouth Physics Professor Lorenza Viola, a co-senior author who is leading the quantum control theory effort and the Quantum Information Initiative at Dartmouth.

"We've now developed the quantum 'firmware' appropriate to control a practically useful quantum memory," added Biercuk. "But vitally, we've shown that with our approach a user may guarantee that error never grows beyond a certain level even after very long times, so long as certain constraints are met. The conditions we establish for the memory to function as advertised then inform system engineers how they can construct an efficient and effective quantum memory. Our method even incorporates a wide variety of realistic experimental imperfections."

Present day computers or classical computers, as they are called, uses bits to store information. A bit is the fundamental unit of information for a classical computer. It can be either On (1) or Off (0). By arranging a series of bits, information or calculations can be carried out by classical computers. This technology is what defines the present day digital age where information is processed in a series of 0s and 1s.

A quantum computer uses a different unit for storing information; a qubit. Qubits are made up of atoms and because of the laws of quantum mechanics, exhibit peculiar behaviors that can be utilized in quantum computing. Instead of storing information in 2 states, qubits can store information in three states; an up state (1), a down state (0), and a superposition state which is both up and down at the same time. This is achieved because of quantum mechanics. Atoms have a spin up stage and a spin down stage that can be interpreted as 1 and 0. But they also can achieve superposition which is both up and down.

In terms of computing power, this means that a quantum computer can theoretically perform a calculation in one step where a classical or digital computer may take several. A classical computer can be programmed to dial a million phone numbers, it will perform this by dialing a phone one million times. A quantum computer can dial the same million numbers all at the same time, in one step.

At the moment there are quantum computers that have been built but because of technological limitations, are as big as a room. And the most a quantum computer have calculated at the moment is finding the factors of the number 15. But given time, just like the massive computers in the early 50s, these will result in smaller, compact computers.

**Quantum Memory**Researchers at the University of Sydney and Dartmouth College have developed a new way to design quantum memory, bringing quantum computers a step closer to reality. The results will appear June 19 in the journal Nature Communications.

Quantum computing may revolutionize information processing, by providing a means to solve problems too complex for traditional computers, with applications in code breaking, materials science and physics. But figuring out how to engineer such a machine, including vital subsystems like quantum memory, remains elusive.

In the worldwide drive to build a useful quantum computer, the simple-sounding task of effectively preserving quantum information in a quantum memory is a major challenge. The same physics that makes quantum computers potentially powerful also makes them likely to experience errors, even when quantum information is just being stored idly in memory. Keeping quantum information "alive" for long periods, while remaining accessible to the computer, is a key problem.

The Sydney-Dartmouth team's results demonstrate a path to what is considered a holy grail in the research community: storing quantum states with high fidelity for exceptionally long times, even hours according to their calculations. Today, most quantum states survive for tiny fractions of a second.

Video: Quantum Computers vs Classical Computers

"Our new approach allows us to simultaneously achieve very low error rates and very long storage times," said co-senior author Dr. Michael J. Biercuk, director of the Quantum Control Laboratory in the University of Sydney's School of Physics and ARC Centre for Engineered Quantum Systems. "But our work also addresses a vital practical issue – providing small access latencies, enabling on-demand retrieval with only a short time lag to extract stored information."

The team's new method is based on techniques to build in error resilience at the level of the quantum memory hardware, said Dartmouth Physics Professor Lorenza Viola, a co-senior author who is leading the quantum control theory effort and the Quantum Information Initiative at Dartmouth.

"We've now developed the quantum 'firmware' appropriate to control a practically useful quantum memory," added Biercuk. "But vitally, we've shown that with our approach a user may guarantee that error never grows beyond a certain level even after very long times, so long as certain constraints are met. The conditions we establish for the memory to function as advertised then inform system engineers how they can construct an efficient and effective quantum memory. Our method even incorporates a wide variety of realistic experimental imperfections."

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