'Cavity protection effect' helps to conserve quantum information

Aug 17, 2014
The quantum system studied at TU Wien (Vienna): a black diamond (center) contains nitrogen atoms, which are coupled to a microwave resonator. Credit: TU Wien

The electronics we use for our computers only knows two different states: zero or one. Quantum systems on the other hand can be in different states at once, they can store a superposition of "zero" and "one". This phenomenon could be used to build ultrafast quantum computers, but there are several technological obstacles that have to be overcome first. The biggest problem is that quantum states are quickly destroyed due to interactions with the environment. At TU Wien (Vienna University of Technology), scientists have now succeeded in using a protection effect to enhance the stability of a particularly promising quantum system.

A Quantum Computer Made of Two Systems

There are various concepts for possible quantum computers. "What we use is a hybrid system of two completely different quantum technologies", says Johannes Majer. Together with his team, he couples microwaves and atoms, investigating and building a new type of quantum memory. The theorists Dmitry Krimer and Stefan Rotter developed a theoretical model describing the complex dynamics in such hybrid quantum systems.

In a microwave resonator, photons are created. They interact with the spin of , which are built into a diamond. The microwave resonator can be used to quickly transport quantum information. The atomic spins in the diamond can store it – at least for a period of several hundred nanoseconds, which is long compared to the time scale on which photons move in the microwave resonator.

"All nitrogen atoms are completely identical. But when they are placed in slightly different surroundings, they have slightly different transition frequencies", says Stefan Putz, PhD-student at Vienna University of Technology. The atomic spins behave like a room full of pendulum clocks. Initially they may oscillate in sync, but as they can never be precisely identical, they eventually lose their rhythm, creating random noise.

Coupling Causes Order

"By creating a strong coupling between the atomic spins and the resonator, it is possible to dramatically prolong the time during which the spins oscillate in strict time – if their energy levels obey the right distribution", says Dmitry Krimer. The atomic spins do not directly interact with each other, but the mere fact that they are collectively coupled to the microwave resonator prevents them from changing into a state in which they cannot be used for processing quantum information any longer. This protection effect considerably enhances the duration in which can be read out from the atomic spins.

"Improving the quantum coherence time with this cavity protection effect opens up many promising applications for our hybrid system", says Johannes Majer. The paper has now been published in Nature Physics.

Explore further: Diamonds are a quantum computer's best friend

More information: Protecting a spin ensemble against decoherence in the strong-coupling regime of cavity QED, Nature Physics, DOI: 10.1038/nphys3050

add to favorites email to friend print save as pdf

Related Stories

The diamond’s quantum memory

Aug 10, 2011

For years, quantum computers have been the holy grail of quantum technology. When a normal computer has to solve a number of problems, it can only execute them one after the other. In contrast, a quantum computer ...

Towards hybrid quantum systems

May 16, 2012

EU-funded scientists made advances in the development of a hybrid quantum system (HQS) by combining different quantum technologies.

Unleashing the power of quantum dot triplets

Jul 24, 2014

Quantum computers have yet to materialise. Yet, scientists are making progress in devising suitable means of making such computers faster. One such approach relies on quantum dots—a kind of artificial atom, ...

Quantum engineering

Aug 13, 2014

It can be difficult to distinguish between basic and applied research in the nascent field of quantum engineering. One person's exploration of quantum systems like atoms and electrons yields another's building ...

A new model for quantum noise

Jun 18, 2014

The National Physical Laboratory (NPL) has published research in Nature Communications that updates one of the most fundamental concepts in the physics of quantum electronic devices - the standard tunnel ...

Recommended for you

First glimpse inside a macroscopic quantum state

2 hours ago

In a recent study published in Physical Review Letters, the research group led by ICREA Prof at ICFO Morgan Mitchell has detected, for the first time, entanglement among individual photon pairs in a beam ...

Theory of the strong interaction verified

16 hours ago

The fact that the neutron is slightly more massive than the proton is the reason why atomic nuclei have exactly those properties that make our world and ultimately our existence possible. Eighty years after ...

3,000 atoms entangled with a single photon

Mar 25, 2015

Physicists from MIT and the University of Belgrade have developed a new technique that can successfully entangle 3,000 atoms using only a single photon. The results, published today in the journal Nature, repres ...

Quantum correlation can imply causation (Update)

Mar 23, 2015

Does taking a drug and then getting better mean that the drug made you better? Did that tax cut really stimulate the economy or did it recover on its own? The problem of answering such questions - of inferring ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.