A lot of research on the fundamentals of quantum computing has been devoted to error correction. Part of the difficulty stems from another of the key properties of quantum systems: Superpositions can only be sustained as long as you dont measure the qubits value. If you make a measurement, the superposition collapses to a definite value: 1 or 0. So how can you find out if a qubit has an error if you dont know what state it is in?
One ingenious scheme involves looking indirectly, by coupling the qubit to another ancilla qubit that doesnt take part in the calculation but that can be probed without collapsing the state of the main qubit itself. Its complicated to implement, though. Such solutions mean that, to construct a genuine logical qubit on which computation with error correction can be performed, you need many physical qubits.
How many? Quantum theorist Aln Aspuru-Guzik of Harvard University estimates that around 10,000 of todays physical qubits would be needed to make a single logical qubit a totally impractical number. If the qubits get much better, he said, this number could come down to a few thousand or even hundreds. Eisert is less pessimistic, saying that on the order of 800 physical qubits might already be enough, but even so he agrees that the overhead is heavy, and for the moment we need to find ways of coping with error-prone qubits.
An alternative to correcting errors is avoiding them or canceling out their influence: so-called error mitigation. Researchers at IBM, for example, are developing schemes for figuring out mathematically how much error is likely to have been incurred in a computation and then extrapolating the output of a computation to the zero noise limit.
Some researchers think that the problem of error correction will prove intractable and will prevent quantum computers from achieving the grand goals predicted for them. The task of creating quantum error-correcting codes is harder than the task of demonstrating quantum supremacy, said mathematician Gil Kalai of the Hebrew University of Jerusalem in Israel. And he adds that devices without error correction are computationally very primitive, and primitive-based supremacy is not possible. In other words, youll never do better than classical computers while youve still got errors.
Others believe the problem will be cracked eventually. According to Jay Gambetta, a quantum information scientist at IBMs Thomas J. Watson Research Center, Our recent experiments at IBM have demonstrated the basicelementsof quantum error correction onsmalldevices, paving the way towards larger-scaledevices where qubits canreliablystorequantum informationfor a long period of time inthepresence of noise. Even so, he admits that a universal fault-tolerant quantum computer, which has to use logical qubits, is still along way off. Such developments make Childs cautiously optimistic. Im sure well see improved experimental demonstrations of [error correction], but I think it will be quite a while before we see it used for a real computation, he said.
For the time being, quantum computers are going to be error-prone, and the question is how to live with that. At IBM, researchers are talking about approximate quantum computing as the way the field will look in the near term: finding ways of accommodating the noise.
This calls for algorithms that tolerate errors, getting the correct result despite them. Its a bit like working out the outcome of an election regardless of a few wrongly counted ballot papers. A sufficiently large and high-fidelity quantum computation should have some advantage [over a classical computation] even if it is not fully fault-tolerant, said Gambetta.
One of the most immediate error-tolerant applications seems likely to be of more value to scientists than to the world at large: to simulate stuff at the atomic level. (This, in fact, was the motivation that led Feynman to propose quantum computing in the first place.) The equations of quantum mechanics prescribe a way to calculate the properties such as stability and chemical reactivity of a molecule such as a drug. But they cant be solved classically without making lots of simplifications.
In contrast, the quantum behavior of electrons and atoms, said Childs, is relatively close to the native behavior of a quantum computer. So one could then construct an exact computer model of such a molecule. Many in the community, including me, believe that quantum chemistry and materials science will be one of the first usefulapplications of such devices, said Aspuru-Guzik, who has been at the forefront of efforts to push quantum computing in this direction.
Quantum simulations are proving their worth even on the very small quantum computers available so far. A team of researchers including Aspuru-Guzik has developed an algorithm that they call the variational quantum eigensolver (VQE), which can efficiently find the lowest-energy states of molecules even with noisy qubits. So far it can only handle very small molecules with few electrons, which classical computers can already simulate accurately. But the capabilities are getting better, as Gambetta and coworkers showed last September when they used a 6-qubit device at IBM to calculate the electronic structures of molecules, including lithium hydride and beryllium hydride. The work was a significant leap forward for the quantum regime, according to physical chemist Markus Reiher of the Swiss Federal Institute of Technology in Zurich, Switzerland. The use of the VQE for the simulation of small molecules is a great example of the possibility of near-term heuristic algorithms, said Gambetta.
But even for this application, Aspuru-Guzik confesses that logical qubits with error correction will probably be needed before quantum computers truly begin to surpass classical devices. I would be really excited when error-corrected quantum computing begins to become a reality, he said.
If we had more than 200 logical qubits, we could do things in quantum chemistry beyond standard approaches, Reiher adds. And if we had about 5,000 such qubits, then the quantum computer would be transformative in this field.
Despite the challenges of reaching those goals, the fast growth of quantum computers from 5 to 50 qubits in barely more than a year has raised hopes. But we shouldnt get too fixated on these numbers, because they tell only part of the story. What matters is not just or even mainly how many qubits you have, but how good they are, and how efficient your algorithms are.
Any quantum computation has to be completed before decoherence kicks in and scrambles the qubits. Typically, the groups of qubits assembled so far have decoherence times of a few microseconds. The number of logic operations you can carry out during that fleeting moment depends on how quickly the quantum gates can be switched if this time is too slow, it really doesnt matter how many qubits you have at your disposal. The number of gate operations needed for a calculation is called its depth: Low-depth (shallow) algorithms are more feasible than high-depth ones, but the question is whether they can be used to perform useful calculations.
Whats more, not all qubits are equally noisy. In theory it should be possible to make very low-noise qubits from so-called topological electronic states of certain materials, in which the shape of the electron states used for encoding binary information confers a kind of protection against random noise. Researchers at Microsoft, most prominently, are seeking such topological states in exotic quantum materials, but theres no guarantee that theyll be found or will be controllable.
Researchers at IBM have suggested that the power of a quantum computation on a given device be expressed as a number called the quantum volume, which bundles up all the relevant factors: number and connectivity of qubits, depth of algorithm, and other measures of the gate quality, such as noisiness. Its really this quantum volume that characterizes the power of a quantum computation, and Gambetta said that the best way forward right now is to develop quantum-computational hardware that increases the available quantum volume.
This is one reason why the much vaunted notion of quantum supremacy is more slippery than it seems. The image of a 50-qubit (or so) quantum computer outperforming a state-of-the-art supercomputer sounds alluring, but it leaves a lot of questions hanging. Outperforming for which problem? How do you know the quantum computer has got the right answer if you cant check it with a tried-and-tested classical device? And how can you be sure that the classical machine wouldnt do better if you could find the right algorithm?
So quantum supremacy is a concept to handle with care. Some researchers prefer now to talk about quantum advantage, which refers to the speedup that quantum devices offer without making definitive claims about what is best. An aversion to the word supremacy has also arisen because of the racial and political implications.
Whatever you choose to call it, a demonstration that quantum computers can do things beyond current classical means would be psychologically significant for the field. Demonstrating an unambiguous quantum advantage will be an important milestone, said Eisert it would prove that quantum computers really can extend what is technologically possible.
That might still be more of a symbolic gesture than a transformation in useful computing resources. But such things may matter, because if quantum computing is going to succeed, it wont be simply by the likes of IBM and Google suddenly offering their classy new machines for sale. Rather, itll happen through an interactive and perhaps messy collaboration between developers and users, and the skill set will evolve in the latter only if they have sufficient faith that the effort is worth it. This is why both IBM and Google are keen to make their devices available as soon as theyre ready. As well as a 16-qubit IBM Q experience offered to anyone who registers online, IBM now has a 20-qubit version for corporate clients, including JP Morgan Chase, Daimler, Honda, Samsung and the University of Oxford. Not only will that help clients discover whats in it for them; it should create a quantum-literate community of programmers who will devise resources and solve problems beyond what any individual company could muster.
For quantum computing to take traction and blossom, we must enable the world to use and to learn it, said Gambetta. This period is for the world of scientists and industry to focus on getting quantum-ready.
See the rest here:
The Era of Quantum Computing Is Here. Outlook: Cloudy ...
- Is Quantum Technology The Future Of The World? - The Coin Republic - January 12th, 2020
- Were approaching the limits of computer power we need new programmers now - The Guardian - January 12th, 2020
- Global Quantum Computing Market: What it got next? Find out with the latest research available at PMI - Pro News Time - January 12th, 2020
- Quantum Computing Technologies Market to Witness Huge Growth by 2020-2025, Latest study reveals - ReportsPioneer - January 12th, 2020
- Podcast: The Overhype and Underestimation of Quantum Computing - insideHPC - January 10th, 2020
- Charles Hoskinson Predicts Economic Collapse, Rise of Quantum Computing, Space Travel and Cryptocurrency in the 2020s - The Daily Hodl - January 10th, 2020
- Google and IBM square off in Schrodingers catfight over quantum supremacy - The Register - January 10th, 2020
- World High Performance Computing (HPC) Markets to 2025 - AI, IoT, and 5G will be Major Drivers for HPC Growth as they Facilitate the Need to Process... - January 10th, 2020
- Tucson Morning Blend Top 5 Tech Trends you'll love this year. Heather Rowe 1:27 - KGUN - January 6th, 2020
- Honeywell names Top 11 Innovations of 2019 - wingsmagazine.com - January 6th, 2020
- 19 Most In-Demand Tech Jobs in Silicon Valley (and the Companies Hiring) - Dice Insights - January 6th, 2020
- January 9th: France will unveil its quantum strategy. What can we expect from this report? - Quantaneo, the Quantum Computing Source - January 4th, 2020
- US Government Looks To Restrict Exports Of AI, Quantum Computing And Self-Driving Tech - WebProNews - January 4th, 2020
- News Content Hub - Five emerging technologies for the 2020s - Riviera Maritime Media - January 4th, 2020
- Superconductor or not? They're exploring the identity crisis of this weird quantum material. - News@Northeastern - January 3rd, 2020
- Year 2019 in Science: History of Humans, Ebola Treatment and Quantum Computing - NewsClick - January 3rd, 2020
- 5 tech that will explode in your life this decade - ETCIO.com - January 3rd, 2020
- Quantum Computing Market Utilities and Recycling In Global 2020 Outlook, Business Strategies, Challenges and Forecasts - Market Research Sheets - January 3rd, 2020
- Quantum Teleportation Has Been Achieved With the Help of Quantum Entanglement - Dual Dove - January 3rd, 2020
- The science fiction that became science fact in 2019 - SYFY WIRE - January 3rd, 2020
- Global Quantum Computing Market to Witness an Outstanding Growth During 2020-2029 - Neptune Pine - January 3rd, 2020
- Quantum Computing Technologies market by Size | Growth | Analysis | Trends and Forecasts to 2020-2025 Bulletin Line - Bulletin Line - January 3rd, 2020
- The Impact of Quantum Computing on Banking will be gigantic says Deltec Bank, Bahamas - Quantaneo, the Quantum Computing Source - December 28th, 2019
- How This Breakthrough Makes Silicon-Based Qubit Chips The Future of Quantum Computing - Analytics India Magazine - December 28th, 2019
- 2020 Will be a Banner Year for AI Custom Chipsets and Heterogenous Computing; Quantum Computing Remains on the Far Horizon - Business Wire - December 28th, 2019
- Top 5: Scientific Breakthroughs That Made 2019 an Unforgettable Year of Human Progress - The Weather Channel - December 28th, 2019
- 2020 will be the beginning of the tech industry's radical revisioning of the physical world - TechCrunch - December 28th, 2019
- IBM and the U. of Tokyo launch quantum computing initiative for Japan | - University Business - December 25th, 2019
- IBM and the University of Tokyo Launch Quantum Computing Initiative for Japan - Martechcube - December 25th, 2019
- AI, 5G, 'ambient computing': What to expect in tech in 2020 and beyond - USA TODAY - December 18th, 2019
- The Quantum Computing Decade Is ComingHeres Why You Should Care - Observer - December 18th, 2019
- Shaping the technology transforming our society - Fermi National Accelerator Laboratory - December 17th, 2019
- Quantum Technology Expert to Discuss Quantum Sensors for Defense Applications at Office of Naval Research (ONR) - Business Wire - December 17th, 2019
- Comrehensive Report : Quantum Computing Market Global Analysis By Latest Trends, Share, Development And Growth By Regions To 2028 - Sound On Sound... - December 17th, 2019
- Anyscale, from the creators of the Ray distributed computing project, launches with $20.6M led by A16Z - TechCrunch - December 17th, 2019
- What WON'T Happen in 2020: 5G Wearables, Quantum Computing, and Self-Driving Trucks to Name a Few - Business Wire - December 16th, 2019
- Quantum computing leaps ahead in 2019 with new power and speed - CNET - December 12th, 2019
- Quantum computing could be the next big security breakthrough - ITProPortal - December 12th, 2019
- Quantum Computers Are the Ultimate Paper Tiger - The National Interest Online - December 12th, 2019
- D-Wave partners with NEC to build hybrid HPC and quantum apps - TechCrunch - December 12th, 2019
- Security leaders fear that quantum computing developments will outpace security technologies - Continuity Central - December 12th, 2019
- D-Wave Announces Promotion of Dr. Alan Baratz to CEO - HPCwire - December 12th, 2019
- Recent Research: Quantum Computing Market with Future Prospects, Key Players SWOT Analysis and Forecast To 2029 - Sound On Sound Fest - December 12th, 2019
- This Week in Tech: What on Earth Is a Quantum Computer? - The New York Times - December 7th, 2019
- Quantum Computers Are About to Forever Change Car Navigation - autoevolution - December 7th, 2019
- Amazon is now offering quantum computing as a service with Braket for AWS - The Verge - December 2nd, 2019
- ColdQuanta's Latest Ultracold Technology Heads to the International Space Station - Business Wire - December 2nd, 2019
- Researchers Discover New Way to Split and Sum Photons with Silicon - UT News | The University of Texas at Austin - December 2nd, 2019
- Archer Materials invited to chair quantum computing session at London conference - Proactive Investors Australia - December 2nd, 2019
- Archer Materials to chair Quantum Computing session at London Quantum.Tech Conference in 2020 - Proactive Investors Australia - November 30th, 2019
- The Future of Computing could be Magnetic - Robert Lea - Medium - November 30th, 2019
- Innovate, and grow - Economic Times - November 30th, 2019
- Tech news: The quantum internet is on the way - IOL - November 22nd, 2019
- Device Puts Photons in the Fast Lane - Optics & Photonics News - November 22nd, 2019
- Race is on to build quantum-proof encryption - Financial Times - November 21st, 2019
- Atos partners with Zapata to deliver complete quantum computing solution to the enterprise - Quantaneo, the Quantum Computing Source - November 20th, 2019
- NTT offers researchers $1 million salaries in bid to lure top talent in cryptography, quantum computing - The Japan Times - November 20th, 2019
- Information overload: The promise and risk of quantum computing - Bulletin of the Atomic Scientists - November 17th, 2019
- D-Wave sticks with its approach to quantum computing - TechCrunch - November 17th, 2019
- Dell Technologies on democratising 5G and the future of quantum computing - ZDNet - November 17th, 2019
- How Serious Is the Threat of Quantum Computing to Crypto? - Finance Magnates - November 17th, 2019
- Superconducting quantum computing - Wikipedia - October 6th, 2019
- Quantum computing | MIT News - October 6th, 2019
- How Do Quantum Computers Work? - sciencealert.com - October 2nd, 2019
- What is Quantum Computing? - Definition from Techopedia - October 2nd, 2019
- How Quantum Computers Work | HowStuffWorks - September 5th, 2019
- Quantum computing could change everything, and IBM is ... - May 15th, 2019
- Quantum Computing - Intel - April 29th, 2019
- IBM expands universities in its quantum computing research ... - April 25th, 2019
- Quantum computing is a marathon not a sprint | VentureBeat - April 22nd, 2019
- The CIO's Guide to Quantum Computing - Smarter With Gartner - April 19th, 2019
- This Startup Just Raised $21 Million To Bring Quantum ... - April 18th, 2019
- What is Quantum Computing ? Top 18 Quantum Computing ... - April 6th, 2019
- The promise of quantum computing - businessinsider.com - March 27th, 2019
- Quantum computing is coming: Heres why we need to get our ... - March 23rd, 2019
- Quantum computing will break your encryption in a few ... - March 21st, 2019
- Microsoft has formed a coalition to promote quantum computing ... - March 19th, 2019
- Quantum computing for everyone | Michael Nielsen - March 12th, 2019
- Ask a Techspert: What is quantum computing? - blog.google - March 6th, 2019
- IBM hits quantum computing milestone, may see 'Quantum ... - March 6th, 2019