Search FQXi

If you are aware of an interesting new academic paper (that has been published in a peer-reviewed journal or has appeared on the arXiv), a conference talk (at an official professional scientific meeting), an external blog post (by a professional scientist) or a news item (in the mainstream news media), which you think might make an interesting topic for an FQXi blog post, then please contact us at with a link to the original source and a sentence about why you think that the work is worthy of discussion. Please note that we receive many such suggestions and while we endeavour to respond to them, we may not be able to reply to all suggestions.

Please also note that we do not accept unsolicited posts and we cannot review, or open new threads for, unsolicited articles or papers. Requests to review or post such materials will not be answered. If you have your own novel physics theory or model, which you would like to post for further discussion among then FQXi community, then please add them directly to the "Alternative Models of Reality" thread, or to the "Alternative Models of Cosmology" thread. Thank you.

Forum Home
Terms of Use

Order posts by:
 chronological order
 most recent first

Posts by the blogger are highlighted in orange; posts by FQXi Members are highlighted in blue.

By using the FQXi Forum, you acknowledge reading and agree to abide by the Terms of Use

 RSS feed | RSS help

Thomas Ray: on 12/2/13 at 16:58pm UTC, wrote It's too bad this important result got buried. Random noise and quantum...

Domenico Oricchio: on 11/1/13 at 9:54am UTC, wrote I am thinking that a quantum ternary digit have more occupation states , so...

Gheorghe-Sorin Paraoanu: on 10/31/13 at 15:59pm UTC, wrote ...Imagine it is deep winter in Finland, where I am based at Aalto...


John Cox: "A proposal for dealing with errors in quantum computers by harnessing a..." in Quantum information...

Steve Dufourny: "There is no proof that the universe can be explained like this like an..." in Schrödinger’s A.I....

Georgina Woodward: "'verisimilitude' is a nice word." in Can We Feel What It’s...

R.H. Joseph: ""[H]ow consciousness plays with quantum mechanics, our theory of the very..." in Can We Feel What It’s...

Jim Snowdon: "If Earth rotated once a year, rather than once every 24 hours, every..." in The Nature of Time

Jim Snowdon: "The constant rotational speed of San Diego is 1,408 kilometers per hour. ..." in The Nature of Time

Steve Dufourny: "If we don t change the global system, we shall add an ocean of chaotical..." in Global Collaboration

Steve Dufourny: "Hi all, The world must absolutelly find adapted solutions , here is the..." in Global Collaboration

click titles to read articles

Schrödinger’s A.I. Could Test the Foundations of Reality
Physicists lay out blueprints for running a 'Wigner's Friend' experiment using an artificial intelligence, built on a quantum computer, as an 'observer.'

Expanding the Mind (Literally): Q&A with Karim Jerbi and Jordan O'Byrne
Using a brain-computer interface to create a consciousness 'add-on' to help test Integrated Information Theory.

Quanthoven's Fifth
A quantum computer composes chart-topping music, programmed by physicists striving to understand consciousness.

The Math of Consciousness: Q&A with Kobi Kremnitzer
A meditating mathematician is developing a theory of conscious experience to help understand the boundary between the quantum and classical world.

Can We Feel What It’s Like to Be Quantum?
Underground experiments in the heart of the Italian mountains are testing the links between consciousness and collapse theories of quantum physics.

October 2, 2022

CATEGORY: Blog [back]
TOPIC: Fighting Noise with Noise: Simulation of motional averaging with a superconducting circuit [refresh]
Bookmark and Share
Login or create account to post reply or comment.

Blogger Gheorghe-Sorin Sorin Paraoanu wrote on Oct. 31, 2013 @ 15:59 GMT
...Imagine it is deep winter in Finland, where I am based at Aalto University, and the temperature outside is -30 degrees Celsius. A nicely warmed sauna at 80 degrees Celsius would surely be welcome for warming up. Getting in the sauna, then directly out in the freezing cold is an "extreme" experience that many people actually enjoy a lot. If you are one of those, and assuming that you spend roughly the same amount of time outside in the cold and in the sauna, the average temperature you see is a perfect 25 degrees Celsius. Welcome to sunny California! Well, not really...

Yet, as it turns out, switching between states with different chemical potential is something that particles in various many-body ensembles experience, and indeed this phenomenon has been seen before in NMR (nuclear magnetic resonance). An experiment recently carried out by our group at Aalto (with theory support from Oulu University) looking into this effect shows that it could have relevance for quantum computation. Quantum computers process information encoded onto "qubits" (or "quantum bits"). For example, the polarization state of photons is typically used in quantum-optics experiments. In our case, we employ the oscillatory states of an electrical circuit, realized with Josephson junctions and superconductors. The quantum bits can not only exist in one or the other of two states (like binary digits 0 and 1), but also as a superposition of both states simultaneously--allowing, in theory, for much more powerful processing.

In our experiment we simulate the effect of switching the chemical potential using a circuit comprising a qubit and a measuring cavity by changing the qubit frequency between two distinct values (J.Li et. al., Nat. Commun. 4, 1420 (2013)). We keep track of this frequency by monitoring the interaction between microwave radiation and the qubit, which results in distinctive lines in the absorption spectrum at certain frequencies.

Motional averaging under a random modulation
Now, you might expect that we would see two spectral lines, one corresponding to each of the frequency extremes--in much the same way as our Finnish sauna fan would register two very different temperatures if he or she jumped from the sauna to the snow. That is indeed what we saw when the switching was done slowly. But surprisingly, when the change was faster than a critical value (the inverse of the qubit frequency separation) the two lines merge into a single one. The image on the right shows motional averaging under a random modulation (pulse pattern in white). The figure presents the spectrum (horizontal axis is frequency) at increasing jump frequencies (vertical axis).

The effect can be interpreted as meaning that our ability of distinguishing between the two values of the qubit frequency is impaired by the fast switching. Indeed, the single (motional-averaged) spectral line is formed precisely when the jumping rate exceeds the bound set by the time-energy uncertainty relation,

Why is this important? One of the biggest hurdles to building a quantum computer is that the quantum effects on which it relies are fragile and can easily be destroyed by decoherence, as the qubits cannot be totally isolated. The motional averaging experiment suggest a new route to improving the decoherence times of the existing qubits. If the noise entering from the environment in such a device fluctuates slowly, it will have a disruptive effect, for example displacing the frequency of the qubit between two extremes. But if this noise can be made faster than a threshold value, the qubit will effectively be at one stable frequency, reducing the so-called dephasing rate. Paradoxically, one can fight noise with even more noise! Indeed, the group has demonstrated that the motional-averaged line preserves the quantum coherence of the original qubit and elementary quantum operations can be performed.

So how fast one has to jump in and out of the sauna to experience a perfect 25 Celsius? According to the calculations in our paper, you have to jump, on average, more than roughly 10 thousand billion times per second!


Gheorghe Sorin Paraoanu is a physicist at Aalto University and a member of FQXi.

Bookmark and Share
report post as inappropriate

Domenico Oricchio wrote on Nov. 1, 2013 @ 09:54 GMT
I am thinking that a quantum ternary digit have more occupation states , so that can represent greater system of the q-bit: is it be possible to obtain a polarized oscillation of plasmons, in an ellipsoidal oscillation? Or to use a spin of a particle with mass?

I am thinking that if the oscillation of the noise is great, then the photon excitation of the noise don't excite the qbit level, so that if there is a high-pass photon filter there is coherence..

Bookmark and Share
report post as inappropriate

Thomas Howard Ray wrote on Dec. 2, 2013 @ 16:58 GMT
It's too bad this important result got buried.

Random noise and quantum discord are quietly leading the charge right now, toward scalable quantum computing that does not depend on a superposition of states.

True, researchers continue to pay lip service to linear superposition as if it is real -- can one defend the idea as other than a superfluous assumption? After all, the...

view entire post

Bookmark and Share
report post as inappropriate

Login or create account to post reply or comment.

Please enter your e-mail address:
Note: Joining the FQXi mailing list does not give you a login account or constitute membership in the organization.