Back to the Future

Scientists have designed a flux capacitator – but it won’t take us ‘Back to the Future’

Physicists have designed an electrical component that breaks time-reversal symmetry. Not quite the time machine from Hollywood, but it could have vital uses.

The technology that allowed Marty McFly to travel back in time in the 1985 movie Back to the Future was the mythical flux capacitor, designed by inventor Doc Brown.

We’ve now developed our own kind of flux capacitor, as detailed recently in Physical Review Letters.

While we can’t send a DeLorean car back in time, we hope it will have important applications in communication technology and quantum computing.

How did we do it? Well it’s all to do with symmetry. There are many kinds of symmetry in science, including one that deals with time reversal.

Time reversal

Time reversal symmetry is a complex sort of symmetry that physicists like to think about, and relies on the imaginary as much as the real.

Suppose you make a movie of an event occurring. You could then ask: “If I edited the movie to run backwards, and showed it to my friends, could they tell?”

This might seem obvious: people don’t usually walk or talk backwards; spilt milk doesn’t spontaneously jump back into its carton; a golf ball doesn’t miraculously launch backwards from the fairway, landing perfectly balanced on the tee at the same moment as the club catches it.

Golf doesn’t look so convincing in reverse. Credit: Tom Stace
Golf doesn’t look so convincing in reverse. Credit: Tom Stace

But at a microscopic level, the story is not that clear. The collision of two billiard balls looks pretty similar in reverse; even more so for the collision of two atoms. A beam of light travelling in one direction obeys exactly the same laws of physics as a beam of light travelling in the opposite direction.

Indeed, the basic equations of physics look essentially the same if we replace time with its negative. This mathematical transformation reverses the flow of time in our equations.

Since the microscopic laws of physics appear to be unchanged under this mathematical transformation, we say the universe possesses time reversal symmetry, even though we cannot actually reverse time in reality. Unlike Doc Brown, we can’t make the clock tick backwards.

There is a conceptual conflict here. At the macroscopic scale, the entropy of the universe – a measure of disorder or randomness – always increases, so that there is an arrow of time.

This is obvious in our everyday experience: a scrambled egg is not reversible. How does this irreversiblity emerge from microscopic laws that are reversible? This remains a mystery.

The circulator circuit

Microscopic reversibility presents an important technological challenge. It complicates the diversion of electronic and radio signals around a circuit.

There are various applications where engineers want electromagnetic signals (such as light or radio waves) in a circuit to behave a bit like cars around a roundabout.

This is pictured below: a signal entering port A of the device should be directed to port B; a signal entering at B should go to port C; and a signal entering port C should be directed to port A, clockwise around the device.

A simple representation of a circulator. Photo Credit: Tom Stace
A simple representation of a circulator. Photo Credit: Tom Stace

One way to do this is to use a network of amplifiers to switch signals as desired. But there is a profound result in quantum mechanics (the “no cloning theorem”) that means that amplification must always add noise, or randomness, to the signal. Sorry audiophiles: a perfect amplifier is impossible.

If the signal is extremely weak, so that additional noise is intolerable, then noiseless circulation is accomplished with a device called a circulator. Such devices are used to separate very weak signals going to and from sensitive electronics, including in radar receivers, or in existing and future quantum computers.

It turns out a device like this must locally break time reversal symmetry. If we made a movie of the signals coming and going from the circulator, and ran the movie backwards, it would look different. For example, we would see a signal entering port B and leaving via port A, rather than via C.

But most devices in a quantum research laboratory, such as mirrors, beam splitters, lasers, atoms do not break time reversal symmetry, so cannot be used as circulators. Something else is needed.

The practical way to break time reversal symmetry for real devices is to introduce a magnetic field. Like a rotating vortex in water, magnetic fields have a circulation, since they arise from electrical currents circulating in an electrical loop.

The magnetic field defines a direction of rotation (clockwise or counterclockwise) for electrically charged particles and thus for electrical signals. So when physicists say that a device breaks time reversal symmetry, they usually mean that there is a magnetic field about somewhere.

Commercial circulators are an anomaly in the world of electronics. Unlike transistors, diodes, capacitors and other circuit elements, basic materials science means that commercial circulators have not been miniaturised, and are still the size of a coin.

A large component: an X-band microwave circulator where the circular arrow on the label indicates the direction that power travels. Photo Credit: Antonio Pedreira/Wikimedia Commons
A large component: an X-band microwave circulator where the circular arrow on the label indicates the direction that power travels. Photo Credit: Antonio Pedreira/Wikimedia Commons

Building them into large-scale integrated microelectronic circuits is therefore a challenge. This will become an increasing problem as we try to fit thousands of qubits on a quantum computer chip, each requiring its own circulator to enable control and read-out.

Our quantum flux capacitor

We have developed a new way of building micrometer-sized circulators that can be fabricated on a microchip.

We figured out how to integrate magnetic flux quanta – the smallest units of magnetic field – with microfabricated capacitors and other superconducting circuit elements, so that time-reversal symmetry can be broken.

This lead to our new circulator proposal. As with conventional circulators, there is a magnetic field present. But because we can use just one magnetic flux quantum, our design can be microscopic.

See the design similarity: (right) the fictional flux capacitor from the movie and (left) a schematic representation of the proposed circulator. Photo Credit: Tom Stace/Screenshot from Back to the Future, Author provided
See the design similarity: (right) the fictional flux capacitor from the movie and (left) a schematic representation of the proposed circulator. Photo Credit: Tom Stace/Screenshot from Back to the Future, Author provided

We’ve nicknamed the device the quantum flux capacitor as its circuit diagram has a passing resemblance to Doc Brown’s mythical invention (which are for sale, sort of).

Sadly for history buffs, our design won’t help much in your DeLorean time machine: it doesn’t reverse time. But its magnetic field does break time-reversal symmetry as advertised and we expect these devices will find applications in future quantum technologies.

Even sooner, they may help in high-bandwidth communications environments like mobile phone base stations in very dense populations, or for ultra-high sensitivity radar where every photon of the electromagnetic field counts.

See the flux capacitor flashing behind Marty in the DeLorean. Credit: GIPHY
See the flux capacitor flashing behind Marty in the DeLorean. Credit: GIPHY

Thomas Stace, Professor in Physics, The University of Queensland and Clemens Müller, Researcher on Quantum Technologies, Swiss Federal Institute of Technology Zurich.

This article first appeared on The Conversation.

Support our journalism by subscribing to Scroll+ here. We welcome your comments at
Sponsored Content BY 

The next Industrial Revolution is here – driven by the digitalization of manufacturing processes

Technologies such as Industry 4.0, IoT, robotics and Big Data analytics are transforming the manufacturing industry in a big way.

The manufacturing industry across the world is seeing major changes, driven by globalization and increasing consumer demand. As per a report by the World Economic Forum and Deloitte Touche Tohmatsu Ltd on the future of manufacturing, the ability to innovate at a quicker pace will be the major differentiating factor in the success of companies and countries.

This is substantiated by a PWC research which shows that across industries, the most innovative companies in the manufacturing sector grew 38% (2013 - 2016), about 11% year on year, while the least innovative manufacturers posted only a 10% growth over the same period.

Along with innovation in products, the transformation of manufacturing processes will also be essential for companies to remain competitive and maintain their profitability. This is where digital technologies can act as a potential game changer.

The digitalization of the manufacturing industry involves the integration of digital technologies in manufacturing processes across the value chain. Also referred to as Industry 4.0, digitalization is poised to reshape all aspects of the manufacturing industry and is being hailed as the next Industrial Revolution. Integral to Industry 4.0 is the ‘smart factory’, where devices are inter-connected, and processes are streamlined, thus ensuring greater productivity across the value chain, from design and development, to engineering and manufacturing and finally to service and logistics.

Internet of Things (IoT), robotics, artificial intelligence and Big Data analytics are some of the key technologies powering Industry 4.0. According to a report, Industry 4.0 will prompt manufacturers globally to invest $267 billion in technologies like IoT by 2020. Investments in digitalization can lead to excellent returns. Companies that have implemented digitalization solutions have almost halved their manufacturing cycle time through more efficient use of their production lines. With a single line now able to produce more than double the number of product variants as three lines in the conventional model, end to end digitalization has led to an almost 20% jump in productivity.

Digitalization and the Indian manufacturing industry

The Make in India program aims to increase the contribution of the manufacturing industry to the country’s GDP from 16% to 25% by 2022. India’s manufacturing sector could also potentially touch $1 trillion by 2025. However, to achieve these goals and for the industry to reach its potential, it must overcome the several internal and external obstacles that impede its growth. These include competition from other Asian countries, infrastructural deficiencies and lack of skilled manpower.

There is a common sentiment across big manufacturers that India lacks the eco-system for making sophisticated components. According to FICCI’s report on the readiness of Indian manufacturing to adopt advanced manufacturing trends, only 10% of companies have adopted new technologies for manufacturing, while 80% plan to adopt the same by 2020. This indicates a significant gap between the potential and the reality of India’s manufacturing industry.

The ‘Make in India’ vision of positioning India as a global manufacturing hub requires the industry to adopt innovative technologies. Digitalization can give the Indian industry an impetus to deliver products and services that match global standards, thereby getting access to global markets.

The policy, thus far, has received a favourable response as global tech giants have either set up or are in the process of setting up hi-tech manufacturing plants in India. Siemens, for instance, is helping companies in India gain a competitive advantage by integrating industry-specific software applications that optimise performance across the entire value chain.

The Digital Enterprise is Siemens’ solution portfolio for the digitalization of industries. It comprises of powerful software and future-proof automation solutions for industries and companies of all sizes. For the discrete industries, the Digital Enterprise Suite offers software and hardware solutions to seamlessly integrate and digitalize their entire value chain – including suppliers – from product design to service, all based on one data model. The result of this is a perfect digital copy of the value chain: the digital twin. This enables companies to perform simulation, testing, and optimization in a completely virtual environment.

The process industries benefit from Integrated Engineering to Integrated Operations by utilizing a continuous data model of the entire lifecycle of a plant that helps to increase flexibility and efficiency. Both offerings can be easily customized to meet the individual requirements of each sector and company, like specific simulation software for machines or entire plants.

Siemens has identified projects across industries and plans to upgrade these industries by connecting hardware, software and data. This seamless integration of state-of-the-art digital technologies to provide sustainable growth that benefits everyone is what Siemens calls ‘Ingenuity for Life’.

Case studies for technology-led changes

An example of the implementation of digitalization solutions from Siemens can be seen in the case of pharma major Cipla Ltd’s Kurkumbh factory.

Cipla needed a robust and flexible distributed control system to dispense and manage solvents for the manufacture of its APIs (active pharmaceutical ingredients used in many medicines). As part of the project, Siemens partnered with Cipla to install the DCS-SIMATIC PCS 7 control system and migrate from batch manufacturing to continuous manufacturing. By establishing the first ever flow Chemistry based API production system in India, Siemens has helped Cipla in significantly lowering floor space, time, wastage, energy and utility costs. This has also improved safety and product quality.

In yet another example, technology provided by Siemens helped a cement plant maximise its production capacity. Wonder Cement, a greenfield project set up by RK Marbles in Rajasthan, needed an automated system to improve productivity. Siemens’ solution called CEMAT used actual plant data to make precise predictions for quality parameters which were previously manually entered by operators. As a result, production efficiency was increased and operators were also freed up to work on other critical tasks. Additionally, emissions and energy consumption were lowered – a significant achievement for a typically energy intensive cement plant.

In the case of automobile major, Mahindra & Mahindra, Siemens’ involvement involved digitalizing the whole product development system. Siemens has partnered with the manufacturer to provide a holistic solution across the entire value chain, from design and planning to engineering and execution. This includes design and software solutions for Product Lifecycle Management, Siemens Technology for Powertrain (STP) and Integrated Automation. For Powertrain, the solutions include SINUMERIK, SINAMICS, SIMOTICS and SIMATIC controls and drives, besides CNC and PLC-controlled machines linked via the Profinet interface.

The above solutions helped the company puts its entire product lifecycle on a digital platform. This has led to multi-fold benefits – better time optimization, higher productivity, improved vehicle performance and quicker response to market requirements.

Siemens is using its global expertise to guide Indian industries through their digital transformation. With the right technologies in place, India can see a significant improvement in design and engineering, cutting product development time by as much as 30%. Besides, digital technologies driven by ‘Ingenuity for Life’ can help Indian manufacturers achieve energy efficiency and ensure variety and flexibility in their product offerings while maintaining quality.


The above examples of successful implementation of digitalization are just some of the examples of ‘Ingenuity for Life’ in action. To learn more about Siemens’ push to digitalize India’s manufacturing sector, see here.

This article was produced on behalf of Siemens by the marketing team and not by the editorial staff.