Quantum computers are largely hypothetical devices that could perform some calculations much more rapidly than conventional computers can. They exploit a property called superposition, which describes a quantum particle’s counterintuitive ability to, in some sense, inhabit more than one physical state at the same time.
But superposition is fragile, and finding ways to preserve it is one of the chief obstacles to developing large, general-purpose quantum computers. In today’s Nature, MIT researchers describe a new approach to preserving superposition in a class of quantum devices built from synthetic diamonds. The work could ultimately prove an important step toward reliable quantum computers.
In most engineering fields, the best way to maintain the stability of a physical system is feedback control. You make a measurement — the current trajectory of an airplane, or the temperature of an engine — and on that basis produce a control signal that nudges the system back toward its desired state.
The problem with using this technique to stabilize a quantum system is that measurement destroys superposition. So quantum-computing researchers have traditionally had to do without feedback.
“Typically, what people do is to use what’s called open-loop control,” says Paola Cappellaro, the Esther and Harold Edgerton Associate Professor of Nuclear Science and Engineering at MIT and senior author on the new paper. “You decide a priori how to control your system and then apply your controller and hope for the best — that you knew enough about your system that the control you applied will do what you thought it should. Feedback should be more robust, because it lets you adapt to what’s going wrong.”
In the Nature paper, Cappellaro and her former PhD student Masashi Hirose, who graduated last year and is now with McKinsey and Company in Tokyo, describe a feedback-control system for maintaining quantum superposition that requires no measurement. “Instead of having a classical controller to implement the feedback, we now use a quantum controller,” Cappellaro explains. “Because the controller is quantum, I don’t need to do a measurement to know what’s going on.”
Vacant expression
Cappellaro and Hirose’s system uses a so-called nitrogen-vacancy center in diamond. A pure diamond consists of carbon atoms arranged in a regular latticework structure. If a carbon nucleus is missing from the lattice where one would be expected, that’s a vacancy. If a nitrogen atom takes the place of a carbon atom in the lattice, and it happens to be adjacent to a vacancy, that’s a nitrogen-vacancy (NV) center.
Associated with every NV center is a group of electrons from the adjacent atoms, which, like all electrons, have a property called spin that describes their magnetic orientation. When subjected to a strong magnetic field — from, say, a permanent magnet positioned above the diamond — an NV center’s electronic spin can be up, down, or a quantum superposition of the two. It can thus represent a quantum bit, or “qubit,” which differs from an ordinary computer bit in its ability to take on not just the values 1 or 0, but both at the same time.
NV centers have several advantages over other candidate qubits. They’re an intrinsic feature of a physical structure, so they dispense with the complex hardware for trapping ions or atoms that other approaches require. And NV centers are natural light emitters, which makes it relatively easy to read information from them. Indeed, the light particles emitted by an NV center may themselves be in superposition, so they provide a way to move quantum information around.
Page 1 of 2
Suggested Items
Real Time with... IPC APEX EXPO 2024: AI Implementation at Omron
04/18/2024 | Real Time with...IPC APEX EXPOEditor Nolan Johnson and Omron Product Manager Nick Fieldhouse discuss the company's focus on AI implementation to enhance customer experience and results. They address programming challenges and how AI can help customers achieve better outcomes with less experience. Omron's AI is compatible with existing systems, facilitating easy upgrades.
Cadence Unveils Palladium Z3 and Protium X3 Systems
04/18/2024 | Cadence Design SystemsThe Palladium Z3 and Protium X3 systems offer increased capacity, and scale from job sizes of 16 million gates up to 48 billion gates, so the largest SoCs can be tested as a whole rather than just partial models, ensuring proper functionality and performance.
Real Time with... IPC APEX EXPO 2024: MYCRONIC's Evolution and New Solutions
04/17/2024 | Real Time with...IPC APEX EXPOHenry Crandall interviews Kevin Clue, the vice president of global sales for MYCRONIC's High Flex division. They discuss the company's evolution, emphasizing its strong customer relationships and its role as a versatile, turnkey solution provider. Kevin unveils new solutions launched at IPC APEX EXPO, including an AI-integrated inspection system and the A40 pick-and-place platform. The conversation also touches on the increased use of AI and deep learning.
Australian Flow Batteries and The SCHMID Group Announce Groundbreaking Memorandum of Understanding
04/17/2024 | SCHMID GroupAustralian Flow Batteries Pty Ltd (AFB), a leader in innovative energy solutions and economical, safe, and reliable power storage, and SCHMID Energy Systems GmbH a company of the German SCHMID Group, a global technology leader with a rich history in delivering innovative solutions across multiple industries including Electronics, Renewables, and Energy Storage sectors, are thrilled to announce the signing of a Memorandum of Understanding (MoU)
Ansys Joins BAE Systems’ Mission Advantage Program to Advance Digital Engineering Across US Department of Defense
04/16/2024 | ANSYSAnsys announced it is working with BAE Systems, Inc., to accelerate the adoption of digital engineering and MBSE across the Department of Defense (DoD).