Forever quantum: physicists demonstrate everlasting quantum coherence

October 14, 2016 by Lisa Zyga, Phys.org feature
(a) Preparation of two-qubit states in a chloroform molecule that exhibit quantum coherence for an arbitrarily long time. (b) Visual representation and (c)-(f) tomographies of the state dynamics. Credit: Silva et al. ©2016 American Physical Society

(Phys.org)—Physicists have implemented the first experimental demonstration of everlasting quantum coherence—the phenomenon that occurs when a quantum system exists in a superposition of two or more states at once. Typically, quantum coherence lasts for only a fraction of a second before decoherence destroys the effect due to interactions between the quantum system and its surrounding environment.

The collaboration of physicists, led by Gerardo Adesso at The University of Nottingham and with members from the UK, Brazil, Italy, and Germany, have published a paper on the demonstration of the extreme resilience of quantum coherence in a recent issue of Physical Review Letters.

"Quantum properties can be exploited for disruptive technologies but are typically very fragile," Adesso told Phys.org. "Here we report an experiment which shows for the first time that quantum coherence in a large ensemble of nuclear spins can be naturally preserved ('frozen') under exposure to strong dephasing noise at room temperature, without external control, and for timescales as long as a second and beyond."

Quantum coherence is an inherently quantum property that arises due to the wave-like nature of matter. Most importantly for potential applications, quantum coherence allows a quantum system to occupy a superposition of states. This trait leads to quantum parallelism, which is the key ingredient that allows some quantum devices to outperform classical ones in a wide range of applications. For instance, many research groups are currently working on harnessing quantum coherence to develop quantum algorithms, quantum cryptography, quantum metrology, and other quantum technologies.

However, a major obstacle to developing these technologies is to overcome the fragile, fleeting nature of quantum coherence. While researchers have developed methods to slow down or correct the effects of decoherence, these methods are generally very resource-demanding.

The method presented in the new study does not attempt to slow down or correct decoherence, but instead it reveals a natural mechanism under which resilience to decoherence spontaneously emerges. The results show that, under certain conditions, quantum coherence remains completely unaffected by common mechanisms of decoherence that typically destroy coherence. The new mechanism was predicted to exist in a study published last year by some of the same authors.

In the new study, the researchers have experimentally observed this effect for the first time. The scientists demonstrated the mechanism in composite systems whose subsystems are all affected by decoherence, yet the overall composite system maintains its quantum coherence for as long as desired.

"The trick lies in the fact that local decoherence acts in a preferred direction, which is perpendicular to the one in which coherence is measured," Adesso explained. "Consequently, the resulting quantum states are overall degraded by such noise, but their observed coherence remains unaffected during the dynamics if the initial conditions are suitably chosen."

The researchers implemented the method using set-ups that involve room-temperature liquid-state nuclear magnetic resonance (NMR) quantum simulators, and demonstrated the effect in two- and four-qubit ensembles.

"We used two different NMR set-ups," said first author Isabela Silva, at the University of São Paulo and The University of Nottingham. "The first, owned by Ivan Oliveira's group in Brazil, consisted of a simple chloroform sample labeled with Carbon-13 to encode the two-qubit system in the hydrogen and carbon nuclei. The four-qubit system was instead a heteronuclear sample specially developed in Steffen Glaser's group in Germany. To manipulate this four-channel heteronuclear system independently, a prototype NMR probe head was also developed. Both systems are affected by natural and independent dephasing channels. Therefore, once initial quantum states satisfying special constraints are prepared, the quantum coherence freezing can be automatically observed, with no need for external control."

The researchers predict that the surprising effect can occur in larger systems composed of any even number of qubits. Odd-numbered qubit systems do not exhibit the resilience because the specific initial conditions supporting the phenomenon cannot be met due to the different geometry of quantum states in such instances.

The researchers also showed that the mechanism appears to be universal, since it does not depend on the specific measure used to quantify the amount of coherence. The researchers expect that this trait will make the mechanism especially useful for future applications.

"The universality paves the way toward designing a novel generation of quantum-enhanced devices able to harness coherence for unscathed performance in realistic and adverse conditions," Adesso said.

Besides technological innovations, the results may also shed light on the quantum coherence that occurs naturally in biological systems, such as the light-harvesting systems in plants. Previous research has shown that some biological systems can maintain for very long times in certain noisy environments.

"The new study raises the possibility that these systems may have evolved an ability to harness natural mechanisms for coherence protection, similar to the one reported here," said coauthor Rosario Lo Franco at the University of Palermo in Italy.

Explore further: Physicists quantify the usefulness of 'quantum weirdness'

More information: Isabela A. Silva et al. "Observation of time-invariant coherence in a room-temperature quantum simulator." Physical Review Letters. DOI: 10.1103/PhysRevLett.117.160402

Also at arXiv:1511.01971 [quant-ph]

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dedereu
1 / 5 (3) Oct 15, 2016
This very fundamental experiment and basic theory, indicates with this perpetual coherence in a transversal basis that the collapse of the wave function postulated by Bohr never happens in a quantum measurement !!
This proof indicates that all the never observed quantum possibilities in a quantum measurement exist real in different parallel universes which are not suppressed if the coherence is everlasting, contrary to the arbitrarycollapse of the wave function od Bohr, but first explained by Everett .
At each nanosecond we have sosies of us multipliing in different parallel universes living all the possible different lifes predicted by the quantum wave functiion but with the same past, if coherence is everlasting !!
Incredible but real if the quantum coherence is everlasting !!
optical
Oct 15, 2016
This comment has been removed by a moderator.
dedereu
3 / 5 (1) Oct 15, 2016
116 years later since its beginning, real quantum mechanic remains fantastic with many more future unexpected discoveries for the basic real properties of our multi-universes !
optical
Oct 15, 2016
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optical
Oct 15, 2016
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dedereu
1 / 5 (1) Oct 15, 2016
The multiverses prevent any arbitrary ideological construct, with a god cutting with a knife the wave function at each measurement to perform the wavefunction collapse, which is so strange that this process is never studied in details precisely quantatively mathematically, in all the published scientific papers, excepted the decoherence process which split the wave function into different universes with even the possibility of ressurection by inversing the decoherence process as observed.
The observation of everlasting coherence is a proof of no wawefunction collpase and prove the reality of everlasting coherence with parallel coherent micro-universes, essential for the extraordinary performance of quantum computers !
Wavefunction collapse to our unique personal universe is identical to the religious old belief that the earth was at the center of our world with the sun and the stars rotating around the earth,
FredJose
1 / 5 (3) Oct 15, 2016
"The new study raises the possibility that these systems may have evolved an ability to harness natural mechanisms for coherence protection, similar to the one reported here," said coauthor Rosario Lo Franco at the University of Palermo in Italy.

PLease, sir! It has taken many years of research by many highly intelligent people to get to this particular point of recognition of the stability of coherence in these types of setups.
Now you want to ascribe all of this ingenuity to chance? This does not make sense.
The customary bow to the god of evolution adds absolutely NOTHING to the great research done by this group, so the only reason for adding it is to confirm allegiance to the religion of the day.
It should be clear that some other highly intelligent living agent was responsible for creating the plants with their superlative light harvesting abilities in the first place. If it wasn't for the discovery that plants have this ability where would your research be today?
dedereu
5 / 5 (2) Oct 15, 2016
It is incredible the number of persons thinking that a god, highly intelligent living agent, is following and controling each atom of each planet to make the living organisms, in the 2 tera 10^12 galaxies of our visible universe, a religious old belief similar to that, 400 years ago, the earth was at the center of our world with the sun and the stars rotating around the earth,

Hyperfuzzy
1 / 5 (2) Oct 16, 2016
We already knew that the E fields may be superimposed by superimposing the field centers. Why is it a puzzle to lock into coherence? And why are you using an undefined item, quanta? What wavelength, object axiomatic structure? Be easier to take off the QM shades, thinking you defined something. Synchronicity, dude!

To collapse the probability wave function, drop QM. Use a succesful model.
torbjorn_b_g_larsson
not rated yet Oct 16, 2016
It is interesting how the coherence immediately switch between quantum and classic correlations as described in the paper (if not in the article), seemingly making a difference between decoherence and collapse.

The thread is filled with dogmatic claims without any support:

@dedereu: Nothing like an absence of collapse can be deduced from the paper, and as I note above they seem to observe the collapse after 0.04 s, phase decoherence after . All what they say is that there is a possibility for indefinite coherence. In fact they seem to observe collapse after 0.04 s, quantum decoherence after 1 s and classical decoherence due to energy exchange with the environment after 12 s. Perhaps you didn't read the paper?

[tbctd]
torbjorn_b_g_larsson
not rated yet Oct 16, 2016
[ctd]

@optical: Multiverse physics are useful (still) theoretical outcomes. They are no different from the infinite number of potentials or other outcomes which are seen in any case of dynamics with differential equation descriptions, such as field theory. If you accept the analogy in electrical circuits, why would you balk at (say) inflationary multiverses?

@Fred: They are describing evolutionary outcomes, which is a process with both deterministic and stochastic outcomes. Exactly like the quantum physics they are basing their evolutionary predictions on, in both cases they wouldn't work if they were based on pure stochastic processes. And these systems have been observed.

As a reflection, it is you who doesn't make sense, trying to describe science as what it is not and preaching insane religious fantasies that we know are not factual on a science site.
optical
Oct 16, 2016
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forumid001
Oct 16, 2016
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