Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Reversing cause and effect is no trouble for quantum computers

20.07.2018

Modelling data in reverse offers hints for how the arrow of time emerges

Watch a movie backwards and you'll likely get confused - but a quantum computer wouldn't. That's the conclusion of researcher Mile Gu at the Centre for Quantum Technologies (CQT) at the National University of Singapore and Nanyang Technological University and collaborators.


Research published in Physical Review X shows that quantum computers can more easily model the reversal of cause and effect -- like following a movie played backwards -- than classical computers. The finding from researchers in Singapore, the United States and Europe may have implications for explaining how we perceive time.

Credit: Aki Honda/Centre for Quantum Technologies, National University of Singapore

Usage Restrictions: Only to be used in reporting on "Causal asymmetry in a quantum world" Physical Review X 8, 031013 (2018) https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.031013

In research published 18 July in Physical Review X, the international team show that a quantum computer is less in thrall to the arrow of time than a classical computer. In some cases, it's as if the quantum computer doesn't need to distinguish between cause and effect at all.

The new work is inspired by an influential discovery made almost ten years ago by complexity scientists James Crutchfield and John Mahoney at the University of California, Davis. They showed that many statistical data sequences will have a built-in arrow of time.

An observer who sees the data played from beginning to end, like the frames of a movie, can model what comes next using only a modest amount of memory about what occurred before. An observer who tries to model the system in reverse has a much harder task - potentially needing to track orders of magnitude more information.

This discovery came to be known as 'causal asymmetry'. It seems intuitive. After all, modelling a system when time is running backwards is like trying to infer a cause from an effect. We are used to finding that more difficult than predicting an effect from a cause. In everyday life, understanding what will happen next is easier if you know what just happened, and what happened before that.

However, researchers are always intrigued to discover asymmetries that are linked to time-ordering. This is because the fundamental laws of physics are ambivalent about whether time moves forwards or in reverse.

"When the physics does not impose any direction on time, where does causal asymmetry - the memory overhead needed to reverse cause and effect - come from?" asks Gu.

The first studies of causal asymmetry used models with classical physics to generate predictions. Crutchfield and Mahoney teamed up with Gu and collaborators Jayne Thompson, Andrew Garner and Vlatko Vedral at CQT to find out whether quantum mechanics changes the situation.

They found that it did. Models that use quantum physics, the team prove, can entirely mitigate the memory overhead. A quantum model forced to emulate the process in reverse-time will always outperform a classical model modelling the process in forward-time.

The work has some profound implications. "The most exciting thing for us is the possible connection with the arrow of time," says Thompson, first author on the work. "If causal asymmetry is only found in classical models, it suggests our perception of cause and effect, and thus time, can emerge from enforcing a classical explanation on events in a fundamentally quantum world," she says.

Next the team wants to understand how this connects to other ideas of time. "Every community has their own arrow of time, and everybody wants to explain where they come from," says Vedral. Crutchfield and Mahoney called causal asymmetry an example of time's 'barbed arrow'.

Most iconic is the 'thermodynamic arrow'. It comes from the idea that disorder, or entropy, will always increase - a little here and there, in everything that happens, until the Universe ends as one big, hot mess. While causal asymmetry is not the same as the thermodynamic arrow, they could be interrelated. Classical models that track more information also generate more disorder. "This hints that causal asymmetry can have entropic consequence," says Thompson.

The results may also have practical value. Doing away with the classical overhead for reversing cause and effect could help quantum simulation. "Like being played a movie in reverse time, sometimes we may be required to make sense of things that are presented in an order that is intrinsically difficult to model. In such cases, quantum methods could prove vastly more efficient than their classical counterparts," says Gu.

###

Reference:

"Causal asymmetry in a quantum world"

Physical Review X 8, 031013 (2018)

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.031013

This work was supported by the National Research Foundation of Singapore and, in particular, NRF Awards No. NRF-NRFF2016-02, No. NRF-CRP14-2014-02, and No. RF2017-NRF-ANR004 VanQuTe, the John Templeton Foundation Grants No. 52095 and No. 54914, Foundational Questions Institute Grant No. FQXi-RFP-1609, and Physics of the Observer Grant (Observer-Dependent Complexity: The Quantum-Classical Divergence over 'What Is Complex?') No. FQXi-RFP-1614, the Oxford Martin School, the Singapore Ministry of Education Tier 1 RG190/17, and the U.S. Army Research Laboratory and the U.S. Army Research Office under Contracts No. W911NF-13-1-0390, No. W911NF-13-1-0340, and No. W911NF-18-1-0028. Much of the collaborative was also made possible by the "Interdisciplinary Frontiers of Quantum and Complexity Science" workshop held in Singapore, funded by the John Templeton Foundation, the Centre for Quantum Technologies, and the Lee Foundation of Singapore.

Researcher contacts:

Mile Gu
Research Assistant Professor, Centre for Quantum Technologies at the National University of Singapore
Assistant Professor, Nanyang Technological University
cqtmileg@nus.edu.sg
+65 6516 5627

Jayne Thompson
Research Fellow, Centre for Quantum Technologies at the National University of Singapore
cqttjed@nus.edu.sg
+65 65166243

Jenny Hogan | EurekAlert!
Further information:
http://dx.doi.org/10.1103/PhysRevX.8.031013

More articles from Information Technology:

nachricht Bursting the clouds for better communication
18.10.2018 | Université de Genève

nachricht Research on light-matter interaction could improve electronic and optoelectronic devices
11.10.2018 | Rensselaer Polytechnic Institute

All articles from Information Technology >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Goodbye, silicon? On the way to new electronic materials with metal-organic networks

Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) together with scientists from Dresden, Leipzig, Sofia (Bulgaria) and Madrid (Spain) have now developed and characterized a novel, metal-organic material which displays electrical properties mimicking those of highly crystalline silicon. The material which can easily be fabricated at room temperature could serve as a replacement for expensive conventional inorganic materials used in optoelectronics.

Silicon, a so called semiconductor, is currently widely employed for the development of components such as solar cells, LEDs or computer chips. High purity...

Im Focus: Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles

Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...

Im Focus: Disrupting crystalline order to restore superfluidity

When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.

We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...

Im Focus: Micro energy harvesters for the Internet of Things

Fraunhofer IWS Dresden scientists print electronic layers with polymer ink

Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...

Im Focus: Dynamik einzelner Proteine

Neue Messmethode erlaubt es Forschenden, die Bewegung von Molekülen lange und genau zu verfolgen

Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Conference to pave the way for new therapies

17.10.2018 | Event News

Berlin5GWeek: Private industrial networks and temporary 5G connectivity islands

16.10.2018 | Event News

5th International Conference on Cellular Materials (CellMAT), Scientific Programme online

02.10.2018 | Event News

 
Latest News

Gravitational Waves Could Shed Light on Dark Matter

22.10.2018 | Physics and Astronomy

Nanocages in the lab and in the computer: how DNA-based dendrimers transport nanoparticles

19.10.2018 | Life Sciences

Thin films from Braunschweig on the way to Mercury

19.10.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>