Skip to main content

A simpler design for quantum computers

A simpler design for quantum computers
A simpler design for quantum computers

Today’s quantum computers are complicated to build, difficult to scale up, and require temperatures colder than interstellar space to operate.

These challenges have led researchers to explore the possibility of building quantum computers that work using photons — particles of light. Photons can easily carry information from one place to another, and photonic quantum computers can operate at room temperature, so this approach is promising. However, although people have successfully created individual quantum “logic gates” for photons, it’s challenging to construct large numbers of gates and connect them in a reliable fashion to perform complex calculations.

Now, Stanford University researchers have proposed a simpler design for photonic quantum computers using readily available components, according to a paper published Nov. 29 in Optica. Their proposed design uses a laser to manipulate a single atom that, in turn, can modify the state of the photons via a phenomenon called “quantum teleportation.” The atom can be reset and reused for many quantum gates, eliminating the need to build multiple distinct physical gates, vastly reducing the complexity of building a quantum computer.

“Normally, if you wanted to build this type of quantum computer, you’d have to take potentially thousands of quantum emitters, make them all perfectly indistinguishable, and then integrate them into a giant photonic circuit,” said Ben Bartlett, a PhD candidate in applied physics and lead author of the paper. “Whereas with this design, we only need a handful of relatively simple components, and the size of the machine doesn’t increase with the size of the quantum program you want to run.”

This remarkably simple design requires only a few pieces of equipment: a fiber optic cable, a beam splitter, a pair of optical switches and an optical cavity.

Fortunately, these components already exist and are even commercially available. They’re also continually being refined since they’re currently used in applications other than quantum computing. For example, telecommunications companies have been working to improve fiber optic cables and optical switches for years.

“What we are proposing here is building upon the effort and the investment that people have put in for improving these components,” said Shanhui Fan, the Joseph and Hon Mai Goodman Professor of the School of Engineering and senior author on the paper. “They are not new components specifically for quantum computation.”

A novel design

The scientists’ design consists of two main sections: a storage ring and a scattering unit. The storage ring, which functions similarly to memory in a regular computer, is a fiber optic loop holding multiple photons that travel around the ring. Analogous to bits that store information in a classical computer, in this system, each photon represents a quantum bit, or “qubit.” The photon’s direction of travel around the storage ring determines the value of the qubit, which like a bit, can be 0 or 1. Additionally, because photons can simultaneously exist in two states at once, an individual photon can flow in both directions at once, which represents a value that is a combination of 0 and 1 at the same time.

The researchers can manipulate a photon by directing it from the storage ring into the scattering unit, where it travels to a cavity containing a single atom. The photon then interacts with the atom, causing the two to become “entangled,” a quantum phenomenon whereby two particles can influence one another even across great distances. Then, the photon returns to the storage ring, and a laser alters the state of the atom. Because the atom and the photon are entangled, manipulating the atom also influences the state of its paired photon.

“By measuring the state of the atom, you can teleport operations onto the photons,” Bartlett said. “So we only need the one controllable atomic qubit and we can use it as a proxy to indirectly manipulate all of the other photonic qubits.”

Because any quantum logic gate can be compiled into a sequence of operations performed on the atom, you can, in principle, run any quantum program of any size using only one controllable atomic qubit. To run a program, the code is translated into a sequence of operations that direct the photons into the scattering unit and manipulate the atomic qubit. Because you can control the way the atom and photons interact, the same device can run many different quantum programs.

“For many photonic quantum computers, the gates are physical structures that photons pass through, so if you want to change the program that’s running, it often involves physically reconfiguring the hardware,” Bartlett said. “Whereas in this case, you don’t need to change the hardware – you just need to give the machine a different set of instructions.”

Stanford postdoctoral scholar Avik Dutt is also co-author of this paper. Fan is a professor of electrical engineering, a member of Stanford Bio-X and an affiliate of the Precourt Institute for Energy.

This research was funded by the U.S. Department of Defense and the U.S. Air Force Office of Scientific Research.

To read all stories about Stanford science, subscribe to the biweekly Stanford Science Digest.

Media Contacts

Taylor Kubota, Stanford News Service: (650) 724-7707, tkubota@stanford.edu



from ScienceBlog.com https://ift.tt/3rnCYaH
Labels:

Comments

Post a Comment

Popular posts from this blog

Wiggling worms suggest link between vitamin B12 and Alzheimer’s

Worms don’t wiggle when they have Alzheimer’s disease. Yet something helped worms with the disease hold onto their wiggle in Professor Jessica Tanis’s lab at the University of Delaware. In solving the mystery, Tanis and her team have yielded new clues into the potential impact of diet on Alzheimer’s, the dreaded degenerative brain disease afflicting more than 6 million Americans. A few years ago, Tanis and her team began investigating factors affecting the onset and progression of Alzheimer’s disease. They were doing genetic research with  C. elegans , a tiny soil-dwelling worm that is the subject of numerous studies. Expression of amyloid beta, a toxic protein implicated in Alzheimer’s disease, paralyzes worms within 36 hours after they reach adulthood. While the worms in one petri dish in Tanis’s lab were rendered completely immobile, the worms of the same age in the adjacent petri dish still had their wiggle, documented as “body bends,” by the scientists. “It was an observa...
Post a Comment
Read more

‘Massive-scale mobilization’ necessary for addressing climate change, scientists say

A year after a global coalition of more than 11,000 scientists declared a climate emergency, Oregon State University researchers who initiated the declaration released an update today that points to a handful of hopeful signs, but shares continued alarm regarding an overall lack of progress in addressing climate risks. “Young people in more than 3,500 locations around the world have organized to push for urgent action,” said Oregon State University’s William Ripple, who co-authored “The Climate Emergency: 2020 in Review,” published today in Scientific American. “And the Black Lives Matter movement has elevated social injustice and equality to the top of our consciousness. “Rapid progress in each of the climate action steps we outline is possible if framed from the outset in the context of climate justice – climate change is a deeply moral issue. We desperately need those who face the most severe climate risks to help shape the response.” One year ago, Ripple, distinguished profess...
Post a Comment
Read more

Ancient Shell Sounds

Abandoned at the mouth of your shelter you quivered apprehensively at our approach, crying out to be held as we proclaimed the exception of your discovery. Sighing wearily as we consigned you to the dusty silence of our archives. But now When I hold you in my hands, I see the face of your purposefully speckled complexion. When I lift you to my ear, I hear the sound of an ancient sea lapping at your shores. When I place you at my lips, I feel the heartbeat of your creator pulsing to my breath. I close my eyes, as you call out to all that you have lost. The shell that was recovered from the Marsoulas cave in the Pyrenees of France (Image Credit: C. Fritz, Muséum d’Histoire naturelle de Toulouse). This poem is inspired by recent research , which has discovered that a large seashell that sat in a French museum for decades is actually a musical instrument used around 18,000 years ago. In 1931, researchers working in southern France unearthed a large seashell at the entr...
Post a Comment
Read more