Controlling Quantum Coherence

One of the first basic quantum calculations utilizing individual molecules was accomplished in 1998 by researchers including Mark Kubinec of UC Berkeley. 

They utilized radio wave pulses to flip the spins of two nuclei in a molecule, with each spin's "up" or "down" orientation storing information in the same way as a "0" or "1" state in a traditional data bit would. 

The combined orientation of the two nuclei—that is, the molecule's quantum state—could only be maintained for short durations in carefully calibrated settings in the early days of quantum computers. 

In other words, the system's coherence was soon destroyed. 

Controlling quantum coherence is the last piece of the scalable quantum computer puzzle. 

Researchers are now working on novel methods to generate and maintain quantum coherence. 

As a result, ultra-sensitive measurement and information processing equipment will be able to operate in ambient or even severe circumstances. 

Joel Moore, a senior faculty scientist at Berkeley Lab and a professor at UC Berkeley, received funding from the Department of Energy in 2018 to establish and lead an Energy Frontier Research Center (EFRC) – the Center for Novel Pathways to Quantum Coherence in Materials (NPQC) – to further those efforts. 

"The EFRCs are a critical tool for DOE because they allow targeted inter-institutional partnerships to make fast progress on cutting-edge scientific issues that are beyond the reach of individual scientists," Moore said. 

Berkeley Lab, UC Berkeley, UC Santa Barbara, Argonne National Laboratory, and Columbia University scientists are leading the way in understanding and manipulating coherence in a range of solid-state systems via the NPQC. 

Their three-pronged strategy focuses on creating new quantum sensing platforms, building two-dimensional materials that host complex quantum states, and investigating methods to precisely regulate a material's electrical and magnetic characteristics via quantum processes. 

The materials science community has the key to solving these issues. 

Developing the capacity to control coherence in real-world settings requires a thorough knowledge of the materials that might be used to create alternative quantum bit (or "qubit"), sensing, or optical technologies. 

Further advances that will contribute to additional DOE expenditures throughout the Office of Science are based on basic findings. 

As the initiative approaches its fourth year, numerous scientific discoveries are setting the foundation for quantum information science advancements. 

Many of NPQC's accomplishments so far have been centered on quantum platforms based on particular faults in a material's structure known as spin defects. 

With the appropriate crystal backdrop, a spin defect may approach complete quantum coherence while also improving resilience and functionality. 

These flaws may be exploited to create high-precision sensor systems. 

Each spin defect reacts to minute changes in the environment, and coherent groups of defects may reach remarkable precision and accuracy. 

However, it's difficult to grasp how coherence develops in a system with multiple spins that interact with one another. 

To address this difficulty, NPQC scientists are turning to diamond, a common material that has shown to be excellent for quantum sensing. 

Each carbon atom in a diamond's crystal structure is linked to four other carbon atoms in nature. 

When one carbon atom is swapped with another or deleted entirely as the diamond's crystal structure develops, the resultant defect may act as an atomic system with a well-defined spin—an inherent type of angular momentum carried by electrons or other subatomic particles. 

Certain imperfections in diamond, like these particles, may have an orientation, or polarization, that is either "spin-up" or "spin-down." 

Norman Yao, a Berkeley Lab faculty scientist and an associate professor of physics at UC Berkeley, and his colleagues developed a 3D system with spins distributed across the volume by designing several distinct spin defects into a diamond lattice. 

The researchers used that setup to create a method for probing the "motion" of spin polarization at very small length scales. 

The researchers discovered that spin travels about in the quantum mechanical system in a similar manner as dye moves in a liquid, using a combination of experimental methods. 

As recently reported in the journal Nature, learning from dyes has shown to be a viable route toward comprehending quantum coherence. 

The multi-defect system not only offers a strong classical framework for understanding quantum dynamics, but it also provides an experimental platform for investigating how coherence works. 

The NPQC platform offers "a particularly controlled example of the interplay between disorder, long-ranged dipolar interactions between spins, and quantum coherence," according to Moore, the NPQC director and a member of the team who has previously researched various types of quantum dynamics.

 

The coherence periods of such spin defects are highly dependent on their immediate surroundings. 

Creating and mapping the strain sensitivity in the structure around individual flaws in diamond and other materials has been the focus of several NPQC discoveries. 

This may show how to manufacture flaws in 3D and 2D materials with the longest feasible coherence durations. 

But how could changes in the defect's coherence be related to changes imposed by pressures on the material itself? 

To find out, NPQC scientists are working on a method for generating distorted regions in a host crystal and measuring strain. 

"If you think of atoms in a lattice as a box spring, you get various outcomes depending on how you press on them," said Martin Holt, a principle scientist at NPQC and group leader in electron and X-ray microscopy at Argonne National Laboratory. 

He and his colleagues provide a direct picture of the distorted regions in a host crystal using the Advanced Photon Source and the Center for Nanoscale Materials, both user facilities at Argonne National Laboratory. 

Until recently, the direction of a defect in a sample was largely random. 

The pictures show which orientations are the most sensitive, indicating that high-pressure quantum sensing is a viable option. 

"It's amazing how you can take something as precious as a diamond and turn it into something useful. 

It's fantastic to have something that's simple enough to grasp fundamental physics yet sophisticated enough to perform advanced physics "Holt said. 

Another aim of this study is to be able to transmit a quantum state, such as a defect in diamond, from one place to another utilizing electrons in a coherent manner. 

Special quantum wires that emerge in atomically thin layers of certain materials are studied by NPQC experts at Berkeley Lab and Argonne Lab. 

The group headed by Feng Wang, a Berkeley Lab faculty senior scientist and UC Berkeley professor, and leader of NPQC's work in atomically thin materials, found superconductivity in one of these systems, a triple layer of carbon sheets. 

"The fact that the same materials may provide both protected one-dimensional conduction and superconductivity offers up some new options for preserving and transmitting quantum coherence," Wang said of the research, which was published in Nature in 2019. 

Multi-defect systems are essential for more than just basic science. 

• They have the potential to be transformational technologies as well. 

• NPQC researchers are investigating how spin defects may be utilized to regulate the material's electrical and magnetic characteristics in new two-dimensional materials that are opening the way for ultra-fast electronics and ultra-stable sensors. 

Recent discoveries have thrown up some unexpected results. 

According to Peter Fischer, a senior scientist and division deputy at Berkeley Lab's Materials Sciences Division, 

• "Fundamental knowledge of nanoscale magnetic materials and their applications in spintronics has already ushered in massive changes in magnetic storage and sensor technology. 

• Quantum coherence in magnetic materials may be the next step toward low-power devices, according to researchers."

The magnetic characteristics of a material are solely determined by the alignment of spins in neighboring atoms. 

Antiferromagnets contain neighboring spins that point in opposing directions and essentially cancel each other out, unlike the perfectly aligned spins in a normal refrigerator magnet or the magnets employed in traditional data storage. 

• Antiferromagnets, as a consequence, do not "act" magnetically and are highly resistant to external perturbations. 

• Researchers have been looking for methods to utilize them in spin-based electronics, where information is carried by spin rather than charge, for a long time. 

Finding a method to alter spin orientation while maintaining coherence is crucial. 

In 2019, NPQC researchers led by James Analytis, a Berkeley Lab faculty scientist and associate professor of physics at UC Berkeley, and postdoc Eran Maniv discovered that applying a small, single pulse of electrical current to tiny antiferromagnet flakes caused the spins to rotate and "switch" their orientation. 

As a consequence, the characteristics of the material may be fine-tuned very fast and accurately. 

• "More experimental observations and some theoretical modeling will be required to understand the mechanics underlying this," Maniv added. 

• "New materials may be able to provide light on how it works. This is the start of a new area of study." 

• The researchers are now attempting to identify the precise process that causes the switching in materials produced and described at Berkeley Lab's Molecular Foundry.

Recent research published in Science Advances and Nature Physics suggests that fine-tuning flaws in a layered material may offer a dependable way to regulate the spin pattern in new device platforms. 

Moore, the NPQC leader, stated, "This is a wonderful illustration of how having numerous flaws allows us to stabilize a switchable magnetic structure." 

• NPQC will expand on this year's accomplishments in its second year of existence. 

• Exploring how numerous flaws interact in two-dimensional materials, as well as researching novel types of one-dimensional structures that may emerge, are among the objectives. 

• These lower-dimensional structures may be used as sensors to detect the smallest-scale characteristics of other materials. 

Focusing on how electric currents may control spin-derived magnetic characteristics will also help to bridge the gap between basic research and applied technology. 

Rapid success on these projects requires a unique blend of methods and experience that can only be developed in a big collaborative setting. 

"You don't build capabilities in a vacuum," Holt said. 

"The NPQC creates a dynamic research environment that propels science forward while also harnessing the work of each lab or site." 

Meanwhile, the research center offers a one-of-a-kind education at the cutting edge of science, as well as chances to train the scientific staff that will drive the future quantum industry. 

The NPQC introduces a new set of questions and objectives to the study of quantum materials' fundamental physics. 

Moore said,  

• "The behavior of electrons in solids is governed by quantum mechanics, and this behavior provides the foundation for most of the contemporary technology we take for granted. 

• However, we are now at the start of the second quantum revolution, in which characteristics such as coherence take center stage, and knowing how to improve these features offers up a new set of material-related issues for us to solve."

~ Jai Krishna Ponnappan

You may also want to read more about Quantum Computing here.

Quantum Computing Application To Detect Alien Life

While quantum computing may take many years to become commonplace in everyday life, the technology has already been enlisted to aid in the hunt for life in outer space. 

Zapata Computing, a quantum software firm, is collaborating with the University of Hull in the United Kingdom on research to assess Zapata's Orquestra quantum workflow platform, which will be used to improve a quantum application intended to identify signs of life in outer space. 

The assessment is not a controlled demonstration of characteristics, according to Dr David Benoit, Senior Lecturer in Molecular Physics and Astrochemistry at the University of Hull, but rather a study using real-world data. 

He said,

 "We're looking at how Orquestra works in realistic processes that utilize quantum computing to give typical real-life data." 

"Rather than a demonstration of skills, we're looking for actual usable data in this endeavor." 

Before the team releases an analysis of the study, the assessment will run for eight weeks. 

According to the parties, this will be the first of many partnerships between Zapata and the University of Hull for quantum astrophysics applications. 

The announcement comes as many quantum computing behemoths, including Google, IBM, Amazon, and Honeywell, were scheduled to attend a White House conference sponsored by the Biden administration to explore developing quantum computing applications. 

In certain instances, academics have resorted to quantum computing to finish tasks that would take too long for traditional computers to complete, and Benoit said the University of Hull is in a similar position. 

"The tests envisioned are still something that a traditional computer can perform," he said, "but, the computing time needed to get the answer has a factorial scale, meaning that bigger applications are likely to take days, months, or years to complete" (along with a very large amount of memory). 

The quantum equivalent is capable of solving such issues in a sub-factorial way (possibly quartic scaling), but this does not necessarily imply that it is quicker for all systems; rather, it means that the computing effort is significantly decreased for big systems. 

We're looking for a scalable method to do precise computations in our application, and quantum computers can help us achieve that. 

What is the scope of the job at hand? 

In 2016, MIT researchers proposed a list of more than 14,000 chemicals that may reveal indications of life in the atmospheres of far-away exoplanets, according to a statement from Zapata. 

However, nothing is presently understood about how these molecules vibrate and spin in response to neighboring stars' infrared light. 

Using new computer models of molecule rotations and vibrations, the University of Hull is attempting to create a library of observable biological fingerprints. 

Though quantum computing models have challenges in fault tolerance and error correction, Benoit claims that researchers are unconcerned about the performance of so-called Noisy Intermediate-Scale Quantum (NISQ) devices. 

"We consider the fact that the findings will be noisy as a beneficial thing since our approach really utilizes the statistical character of the noise/errors to try to get an accurate answer," he added. 

"Clearly, the better the mistake correction or the quieter the equipment, the better the result." 

However, utilizing Orquestra allows us to possibly switch platforms without having to re-implement significant portions of the code, which means we can easily compute with better hardware as it becomes available." 

Orquestra will enable researchers "produce important insights" from NISQ devices, according to Benoit, and researchers will be able to "create applications that utilize these NISQ devices today with the potential to exploit the more powerful quantum devices of the future." 

As a consequence, scientists should be able to do "very precise estimates of the fundamental variable determining atom-atom interactions — electrical correlation," which may enhance their capacity to identify the building elements of life in space. This is critical because even basic molecules like oxygen or nitrogen have complicated interactions that require very precise computations."

~ Jai Krishna Ponnappan

You may also want to read more about Quantum Computing here.

Fault Tolerance For Quantum Computing Errors

 

Scientists working on quantum computers—dream machines that might solve problems that would exceed any supercomputer—are learning to identify and fix their errors like a kid learns arithmetic. 

In the most recent stage, a team showed a method for detecting mistakes in the setup of a quantum bit, or qubit, that is guaranteed not to exacerbate the problem. 

Such "fault tolerance" is a crucial step toward the ultimate aim of keeping fussy qubits alive long enough to be controlled. 

“It seems to be a genuine watershed moment,” says Scott Aaronson, a theoretical computer scientist at the University of Texas at Austin who wasn't involved in the research. 

“We knew it was just a matter of time until someone did something like this.” 

However, John Martinis, an experimental physicist at the University of California, Santa Barbara, wonders whether the latest study's authors are exaggerating their findings. 

He describes it as a "really good step. But it's just a first step.” 

A traditional computer uses small electrical switches, or bits, that can be set to 0 or 1, while a quantum computer uses qubits that can be set to 0 and 1 at the same time. 

A qubit may be a single ion spinning one way, the other, or both directions at the same time, or a small circuit of superconducting metal with two distinct energy states. 

• A quantum computer can encode all of the possible solutions to particular problems as quantum waves sloshing across the qubits thanks to such both-ways-at-once states. 

• Interference cancels out the incorrect answers, allowing the correct solution to emerge. 

• Such methods would allow a big quantum computer to rapidly factor enormous numbers, which is difficult for a regular computer to do, and therefore defeat encryption systems used to secure data on the internet. 

However, even the tiniest disturbance may destabilize a qubit's fragile condition. 

• If a qubit were like a regular bit, researchers could simply duplicate it and count the majority to keep it in the correct condition. 

• If a duplicate does flip, adding up several subsets of the bits (so-called parity tests) will disclose which one it is. 

Quantum theory, on the other hand, prohibits the copying of one qubit's state onto another. 

• Worse, every effort to test a qubit to determine if it is in the proper state causes it to collapse to one of two states: 0 or 1. 

• Researchers circumvent these issues by using entanglement, a quantum link that enables them to distribute the state of an initial "logical" qubit—the object that will ultimately execute the required operation—across many physical qubits. 

• A 0-and-1 state of one qubit, for example, may be extended to three qubits in a condition in which all three are 0 at the same time. 

• Researchers may then entangle additional ancillary qubits with the group and measure the ancillary qubits to identify faults in the main qubits—without ever touching them—in a quantum version of parity checks. 

In fact, the method is considerably more complex since developers must avoid two kinds of errors: 

1. bit flips 
2. and phase flips. 

Despite this, scientists have made progress. 

In June, Google researchers using superconducting qubits demonstrated that spreading a logical qubit over as many as 11 physical qubits with 10 ancillas may decrease the incidence of one kind of mistake but not both at the same time. 

Now, physicists Laird Egan and Christopher Monroe of the University of Maryland (UMD) in College Park, together with others, have shown a method that simultaneously corrects both kinds of flips—and therefore any mistake. 

Individual ytterbium ions are trapped in an electromagnetic field on the chip's surface to form qubits. 

• The researchers utilized nine ions to encode a single logical qubit, as well as four more ions to keep track of the primary ones. 

• Most importantly, in certain respects, the encoded logical qubit outperformed the physical ones on which it is based. 

• The researchers, for example, were able to prepare either the logical 0 or logical 1 state 99.67 percent of the time, which is higher than the 99.54 percent for individual qubits. 

Monroe, creator of IonQ, a firm creating ion-based quantum computers, says, “This is truly the first time where the quality of the [logical] qubit is greater than the components that encode it.”

However, that the encoded qubit did not outperform the individual ions in every manner. 

Instead, the true breakthrough is proving fault tolerance, which implies that the error-correcting mechanism does not create more mistakes than it corrects. 

Fault tolerance is the design concept that prevents mistakes from spreading.

Martinis, on the other hand, has reservations about the term's usage. 

Researchers must also accomplish two additional things, in order to claim genuine fault-tolerant mistake correction. 

• They must demonstrate that as the number of physical qubits grows, the mistakes in a logical qubit become exponentially less. 

• They must also demonstrate that they can measure the auxiliary qubits frequently in order to keep the logical qubit stable, he adds. 

Those are the apparent next steps for the UMD and IonQ teams.

He points out that in order for the encoded logical qubit to outperform the underlying physical qubits in every manner, the latter must first have a low enough error rate. 

~ Jai Krishna Ponnappan

You may also want to read more about Quantum Computing here.

Open Source Quantum Computing Software SDK

Cambridge Quantum has released the newest edition of their hardware-agnostic quantum software development kit, TKET (pronounced "ticket"), as an open source project. 

Open-sourcing provides for more code openness, faster problem reporting, and more sophisticated integrations. 

Under the permissive Apache 2.0 license, members of the quantum software community will be free to contribute their own contributions or draw inspiration and build their own enhancements.

Extensions on the pytket-extensions GitHub repository: https://github.com/CQCL/pytket-extensions

Documentation: https://cqcl.github.io/pytket/build/html/index.html

Extension Documentation: https://cqcl.github.io/pytket/build/html/extensions/index.html

The move comes as the quantum computing industry shifts its focus away from the race to build high-qubit computers and toward the software that will be required to program these systems and set them to work on particular tasks. 

Christian Bauer, Theory Group Leader and PI of Quantum Computing for the Physics Division of Lawrence Berkeley National Laboratory, identified software and the overall challenge of programming quantum computers as an issue that is currently preventing the sector from reaching its full potential during a presentation at Questex's Sensors Converge event last week. 

Companies like Classiq and Quantum Machines have lately brought this problem to light. 

In a statement, Cambridge Quantum stated, 

"Making all the source code accessible to the community enables faster integration, modification, and problem tracking from all users." 

“Under the permissive Apache 2.0 license, any members of the quantum software community will be free to make their own contributions and create their own modifications to the codebase.” 

TKET is also interoperable with other quantum languages such as Qiskit, Cirq, Q#, and others through extension modules, according to the firm. 

Cambridge seems to be on track to play a larger role in this development. 

Honeywell stated in June that it will combine its quantum computing business with Cambridge Quantum, a firm in which it already had a stake, and spend an additional $270 million to $300 million in the spin-off that would emerge. 

The transaction is anticipated to be completed in the fourth quarter. 

“We originally announced that TKET will be accessible on a ‘open-access' basis earlier this year, with a promise to become completely open-sourced by the end of 2021,” Cambridge Quantum CEO Ilyas Khan said in a statement on the open source availability. 

In the meanwhile, he added, the company's developer community has grown at a "amazing" rate. 

“Minimizing gate count and execution time are extremely essential in this Noisy Intermediate Scale Quantum (NISQ) era,” said Ross Duncan, CQ's Head of Software. 

TKET blends high-level hardware-agnostic quantum circuit optimisation with target-specific compilation steps for the quantum device of choice. 

This allows users of quantum computing to travel easily across platforms while retaining excellent performance. 

Users should concentrate on creating quantum applications rather than changing code to accommodate the quirks of certain hardware. 

At the same time, we assist quantum computing hardware manufacturers in ensuring that their processors provide the highest possible performance.

About Cambridge Quantum Computing

Founded in 2014 and backed by some of the world’s leading quantum computing companies, CQC is a global leader in quantum software and quantum algorithms, enabling clients to achieve the most out of rapidly evolving quantum computing hardware. CQC has offices in the UK, USA and Japan. 

For more information, visit CQC at http://www.cambridgequantum.com 

~ Jai Krishna Ponnappan

You may also want to read more about Quantum Computing here.