Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > Uncovering the hidden “noise” that can kill qubits: New detection tool could be used to make quantum computers robust against unwanted environmental disturbances

MIT and Dartmouth College researchers developed a tool that detects new characteristics of non-Gaussian “noise” that can destroy the fragile quantum superposition state of qubits, the fundamental components of quantum computers.

Image courtesy of the researchers
MIT and Dartmouth College researchers developed a tool that detects new characteristics of non-Gaussian “noise” that can destroy the fragile quantum superposition state of qubits, the fundamental components of quantum computers. Image courtesy of the researchers

Abstract:
MIT and Dartmouth College researchers have demonstrated, for the first time, a tool that detects new characteristics of environmental “noise” that can destroy the fragile quantum state of qubits, the fundamental components of quantum computers. The advance may provide insights into microscopic noise mechanisms to help engineer new ways of protecting qubits.

Uncovering the hidden “noise” that can kill qubits: New detection tool could be used to make quantum computers robust against unwanted environmental disturbances

Cambridge, MA | Posted on September 17th, 2019

Qubits can represent the two states corresponding to the classic binary bits, a 0 or 1. But, they can also maintain a “quantum superposition” of both states simultaneously, enabling quantum computers to solve complex problems that are practically impossible for classical computers.

But a qubit’s quantum “coherence” — meaning its ability to maintain the superposition state — can fall apart due to noise coming from environment around the qubit. Noise can arise from control electronics, heat, or impurities in the qubit material itself, and can also cause serious computing errors that may be difficult to correct.

Researchers have developed statistics-based models to estimate the impact of unwanted noise sources surrounding qubits to create new ways to protect them, and to gain insights into the noise mechanisms themselves. But, those tools generally capture simplistic “Gaussian noise,” essentially the collection of random disruptions from a large number of sources. In short, it’s like white noise coming from the murmuring of a large crowd, where there’s no specific disruptive pattern that stands out, so the qubit isn’t particularly affected by any one particular source. In this type of model, the probability distribution of the noise would form a standard symmetrical bell curve, regardless of the statistical significance of individual contributors.

In a paper published today in the journal Nature Communications, the researchers describe a new tool that, for the first time, measures “non-Gaussian noise” affecting a qubit. This noise features distinctive patterns that generally stem from a few particularly strong noise sources.

The researchers designed techniques to separate that noise from the background Gaussian noise, and then used signal-processing techniques to reconstruct highly detailed information about those noise signals. Those reconstructions can help researchers build more realistic noise models, which may enable more robust methods to protect qubits from specific noise types. There is now a need for such tools, the researchers say: Qubits are being fabricated with fewer and fewer defects, which could increase the presence of non-Gaussian noise.

“It’s like being in a crowded room. If everyone speaks with the same volume, there is a lot of background noise, but I can still maintain my own conversation. However, if a few people are talking particularly loudly, I can’t help but lock on to their conversation. It can be very distracting,” says William Oliver, an associate professor of electrical engineering and computer science, professor of the practice of physics, MIT Lincoln Laboratory Fellow, and associate director of the Research Laboratory for Electronics (RLE). “For qubits with many defects, there is noise that decoheres, but we generally know how to handle that type of aggregate, usually Gaussian noise. However, as qubits improve and there are fewer defects, the individuals start to stand out, and the noise may no longer be simply of a Gaussian nature. We can find ways to handle that, too, but we first need to know the specific type of non-Gaussian noise and its statistics.”

“It is not common for theoretical physicists to be able to conceive of an idea and also find an experimental platform and experimental colleagues willing to invest in seeing it through,” says co-author Lorenza Viola, a professor of physics at Dartmouth. “It was great to be able to come to such an important result with the MIT team.”

Joining Oliver and Viola on the paper are: first author Youngkyu Sung, Fei Yan, Jack Y. Qiu, Uwe von Lüpke, Terry P. Orlando, and Simon Gustavsson, all of RLE; David K. Kim and Jonilyn L. Yoder of the Lincoln Laboratory; and Félix Beaudoin and Leigh M. Norris of Dartmouth.

Pulse filters

For their work, the researchers leveraged the fact that superconducting qubits are good sensors for detecting their own noise. Specifically, they use a “flux” qubit, which consists of a superconducting loop that is capable of detecting a particular type of disruptive noise, called magnetic flux, from its surrounding environment.

In the experiments, they induced non-Gaussian “dephasing” noise by injecting engineered flux noise that disturbs the qubit and makes it lose coherence, which in turn is then used as a measuring tool. “Usually, we want to avoid decoherence, but in this case, how the qubit decoheres tells us something about the noise in its environment,” Oliver says.

Specifically, they shot 110 “pi-pulses” — which are used to flip the states of qubits — in specific sequences over tens of microseconds. Each pulse sequence effectively created a narrow frequency “filter” which masks out much of the noise, except in a particular band of frequency. By measuring the response of a qubit sensor to the bandpass-filtered noise, they extracted the noise power in that frequency band.

By modifying the pulse sequences, they could move filters up and down to sample the noise at different frequencies. Notably, in doing so, they tracked how the non-Gaussian noise distinctly causes the qubit to decohere, which provided a high-dimensional spectrum of the non-Gaussian noise.

Error suppression and correction

The key innovation behind the work is carefully engineering the pulses to act as specific filters that extract properties of the “bispectrum,” a two-dimension representation that gives information about distinctive time correlations of non-Gaussian noise.

Essentially, by reconstructing the bispectrum, they could find properties of non-Gaussian noise signals impinging on the qubit over time — ones that don’t exist in Gaussian noise signals. The general idea is that, for Gaussian noise, there will be only correlation between two points in time, which is referred to as a “second-order time correlation.” But, for non-Gaussian noise, the properties at one point in time will directly correlate to properties at multiple future points. Such “higher-order” correlations are the hallmark of non-Gaussian noise. In this work, the authors were able to extract noise with correlations between three points in time.

This information can help programmers validate and tailor dynamical error suppression and error-correcting codes for qubits, which fixes noise-induced errors and ensures accurate computation.

Such protocols use information from the noise model to make implementations that are more efficient for practical quantum computers. But, because the details of noise aren’t yet well-understood, today’s error-correcting codes are designed with that standard bell curve in mind. With the researchers’ tool, programmers can either gauge how their code will work effectively in realistic scenarios or start to zero in on non-Gaussian noise.

Keeping with the crowded-room analogy, Oliver says: “If you know there’s only one loud person in the room, then you’ll design a code that effectively muffles that one person, rather than trying to address every possible scenario.”

###

Written by Rob Matheson, MIT News Office

####

For more information, please click here

Contacts:
Abby Abazorius, MIT News Office
617.253.2709

Copyright © Massachusetts Institute of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

Quantum Physics

HKU physicists found signatures of highly entangled quantum matter July 22nd, 2022

Quantum network nodes with warm atoms June 24th, 2022

Undergrads begin summer quantum research with support from Moore Foundation, Chicago region universities, national labs: Inaugural cohort of students join quantum research labs around the Midwest, planting the seeds for a diverse and inclusive quantum workforce June 17th, 2022

News and information

Biology’s hardest working pigments and ‘MOFs’ might just save the climate: A range of processes that currently depend on fossil fuels but are really hard to electrify will depend on the development of genuinely clean fuels, and for that to happen, much more efficient catalysts wi July 22nd, 2022

Generating power where seawater and river water meet July 22nd, 2022

First electric nanomotor made from DNA material: Synthetic rotary motors at the nanoscale perform mechanical work July 22nd, 2022

At the water’s edge: Self-assembling 2D materials at a liquid–liquid interface: Scientists find a simple way to produce heterolayer coordination nanosheets, expanding the diversity of 2D materials July 22nd, 2022

Physics

Led by Columbia Engineering, researchers build longest, highly conductive molecular nanowire: The 2.6nm-long single molecule wire has quasi-metallic properties and shows an unusual increase of conductance as the wire length increases; its excellent conductivity holds great promis July 8th, 2022

Flexing the power of a conductive polymer: A new material holds promise for the next generation of organic electronics June 24th, 2022

Possible Futures

Biology’s hardest working pigments and ‘MOFs’ might just save the climate: A range of processes that currently depend on fossil fuels but are really hard to electrify will depend on the development of genuinely clean fuels, and for that to happen, much more efficient catalysts wi July 22nd, 2022

Generating power where seawater and river water meet July 22nd, 2022

First electric nanomotor made from DNA material: Synthetic rotary motors at the nanoscale perform mechanical work July 22nd, 2022

At the water’s edge: Self-assembling 2D materials at a liquid–liquid interface: Scientists find a simple way to produce heterolayer coordination nanosheets, expanding the diversity of 2D materials July 22nd, 2022

Chip Technology

The best semiconductor of them all? Researchers have found a material that can perform much better than silicon. The next step is finding practical and economic ways to make it July 22nd, 2022

Buckyballs on gold are less exotic than graphene July 22nd, 2022

Quantum computer works with more than zero and one: Quantum digits unlock more computational power with fewer quantum particles July 22nd, 2022

At the water’s edge: Self-assembling 2D materials at a liquid–liquid interface: Scientists find a simple way to produce heterolayer coordination nanosheets, expanding the diversity of 2D materials July 22nd, 2022

Quantum Computing

Quantum computer works with more than zero and one: Quantum digits unlock more computational power with fewer quantum particles July 22nd, 2022

Optical demonstration of quantum fault-tolerant threshold July 8th, 2022

CEA & Partners Present ‘Powerful Step Towards Industrialization’ Of Linear Si Quantum Dot Arrays Using FDSOI Material at VLSI Symposium: Invited paper reports 3-step characterization chain and resulting methodologies and metrics that accelerate learning, provide data on device pe June 17th, 2022

University of Illinois Chicago joins Brookhaven Lab's Quantum Center June 10th, 2022

Discoveries

HKU physicists found signatures of highly entangled quantum matter July 22nd, 2022

How different cancer cells respond to drug-delivering nanoparticles: The findings of a large-scale screen could help researchers design nanoparticles that target specific types of cancer July 22nd, 2022

The best semiconductor of them all? Researchers have found a material that can perform much better than silicon. The next step is finding practical and economic ways to make it July 22nd, 2022

Buckyballs on gold are less exotic than graphene July 22nd, 2022

Announcements

Quantum computer works with more than zero and one: Quantum digits unlock more computational power with fewer quantum particles July 22nd, 2022

Biology’s hardest working pigments and ‘MOFs’ might just save the climate: A range of processes that currently depend on fossil fuels but are really hard to electrify will depend on the development of genuinely clean fuels, and for that to happen, much more efficient catalysts wi July 22nd, 2022

Generating power where seawater and river water meet July 22nd, 2022

First electric nanomotor made from DNA material: Synthetic rotary motors at the nanoscale perform mechanical work July 22nd, 2022

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters

Buckyballs on gold are less exotic than graphene July 22nd, 2022

Quantum computer works with more than zero and one: Quantum digits unlock more computational power with fewer quantum particles July 22nd, 2022

Biology’s hardest working pigments and ‘MOFs’ might just save the climate: A range of processes that currently depend on fossil fuels but are really hard to electrify will depend on the development of genuinely clean fuels, and for that to happen, much more efficient catalysts wi July 22nd, 2022

Generating power where seawater and river water meet July 22nd, 2022

Research partnerships

Crystal phase engineering offers glimpse of future potential, researchers say July 15th, 2022

New technology helps reveal inner workings of human genome June 24th, 2022

Boron nitride nanotube fibers get real: Rice lab creates first heat-tolerant, stable fibers from wet-spinning process June 24th, 2022

Undergrads begin summer quantum research with support from Moore Foundation, Chicago region universities, national labs: Inaugural cohort of students join quantum research labs around the Midwest, planting the seeds for a diverse and inclusive quantum workforce June 17th, 2022

Quantum nanoscience

Scientists capture a ‘quantum tug’ between neighboring water molecules: Ultrafast electrons shed light on the web of hydrogen bonds that gives water its strange properties, vital for many chemical and biological processes July 8th, 2022

Undergrads begin summer quantum research with support from Moore Foundation, Chicago region universities, national labs: Inaugural cohort of students join quantum research labs around the Midwest, planting the seeds for a diverse and inclusive quantum workforce June 17th, 2022

Bumps could smooth quantum investigations: Rice University models show unique properties of 2D materials stressed by contoured substrates June 10th, 2022

An atomic-scale window into superconductivity paves the way for new quantum materials: New technique helps researchers understand unconventional superconductors June 3rd, 2022

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project