Recent comments from SciRate

Bassam Helou Sep 22 2017 17:21 UTC

The initial version of the article does not adequately and clearly explain how certain equations demonstrate whether a particular interpretation of QM violates the no-signaling condition.
A revised and improved version is scheduled to appear on September 25.

James Wootton Sep 21 2017 05:41 UTC

What does this imply for I'm guessing they still regard it as valid (it is ref [14]), but just too hard to implement for now.

Ben Criger Sep 08 2017 08:09 UTC

Oh look, there's another technique for decoding surface codes subject to X/Z correlated errors:

Aram Harrow Sep 06 2017 07:54 UTC

The paper only applies to conformal field theories, and such a result cannot hold for more general 1-D systems by 0705.4077 and other papers (assuming standard complexity theory conjectures).

Felix Leditzky Sep 05 2017 21:27 UTC

Thanks for the clarification, Philippe!

Philippe Faist Sep 05 2017 21:09 UTC

Hi Felix, thanks for the good question.

We've found it more convenient to consider trace-nonincreasing and $\Gamma$-sub-preserving maps (and this is justified by the fact that they can be dilated to fully trace-preserving and $\Gamma$-preserving maps on a larger system). The issue arises because

Felix Leditzky Sep 05 2017 19:02 UTC

What is the reason/motivation to consider trace-non-increasing maps instead of trace-preserving maps in your framework and the definition of the coherent relative entropy?

Steve Flammia Aug 30 2017 22:30 UTC

Thanks for the reference Ashley. If I understand your paper, you are still measuring stabilizers of X- and Z-type at the top layer of the code. So it might be that we can improve on the factor of 2 that you found if we tailor the stabilizers to the noise bias at the base level.

Ashley Aug 30 2017 22:09 UTC

We followed Aliferis and Preskill's approach in [][1] and found that the fault-tolerant threshold for the surface code was increased by approximately a factor of two, from around 0.75 per cent to 1.5 per cent for a bias of 10 to 100.


Stephen Bartlett Aug 30 2017 21:55 UTC

Following on from Steve's comments, it's possible to use the bias-preserving gate set in Aliferis and Preskill directly to do the syndrome extraction, as you build up a CNOT gadget, but such a direct application of your methods would be very complicated and involve a lot of gate teleportation. If y

Steve Flammia Aug 30 2017 21:38 UTC

We agree that finding good syndrome extraction circuits if an important question. At the moment we do not have such circuits, though we have started to think about them. We are optimistic that this can be done in principle, but it remains to be seen if the circuits can be made sufficiently simple to

John Preskill Aug 30 2017 14:48 UTC

Hi Steves and David. When we wrote our viewpoint was that a gate with highly biased (primarily Z) noise would need to commute with Z. So we built our fault-tolerant gadgets from such gates, along with preparations and measurements in the X basis.

Can you easily ext

Steve Flammia Aug 30 2017 07:29 UTC

We haven't tried the Wen model yet. We thought about doing it, but decided to try this first. When it worked as well as it did we just didn't bother trying the Wen model, but it's a natural question, and I am curious about the answer.

James Wootton Aug 30 2017 05:51 UTC

Seems so obvious now you say it! Well done for trying this out.

Do you know how the results compare to Wen style stabilizers, where both plaquette and vertex stabilizers alternate between two Paulis? I guess using Y and Z would be best for biased noise, given your results.

Travis Scholten Aug 23 2017 14:30 UTC

Wanted to let you know this paper has been updated with new technical results. In particular, we have provided a new section which gives a generalization of [local asymptotic normality]( that is applicable to models with convex constraints (wh

Abhinav Deshpande Aug 07 2017 19:40 UTC

+1 for "Alisha" and "Babu"! :D

Māris Ozols Aug 03 2017 09:34 UTC

If I'm not mistaken, what you describe here is equivalent to the [QR decomposition][1]. The matrices $R_{ij}$ that act non-trivially only in a two-dimensional subspace are known as [Givens rotations][2]. The fact that any $n \times n$ unitary can be decomposed as a sequence of Givens rotations is ex

gae Jul 26 2017 21:19 UTC

For those interested in the literature on teleportation simulation of quantum channels, a detailed and *comprehensive* review is provided in Supplementary Note 8 of
The note describes well the t

Maciej Malinowski Jul 26 2017 15:56 UTC

In what sense is the ground state for large detuning ordered and antiferromagnetic? I understand that there is symmetry breaking, but other than that, what is the fundamental difference between ground states for large negative and large positive detunings? It seems to be they both exhibit some order

Stefano Pirandola Jul 26 2017 15:28 UTC

The performance of the memory assisted MDI-QKD with "quasi-EPR" sources is remarkable. It improves the key rate by 5 orders of magnitude over the PLOB bound at about 600 km (take a look at Figure 4).

Māris Ozols Jul 26 2017 11:07 UTC

Conway's list still has four other $1000 problems left:

SHUAI ZHANG Jul 26 2017 00:20 UTC

I am still working on improving this survey. If you have any suggestions, questions or find any mistakes, please do not hesitate to contact me:

Alvaro M. Alhambra Jul 24 2017 16:10 UTC

This paper has just been updated and we thought it would be a good
idea to advertise it here. It was originally submitted a year ago, and
it has now been essentially rewritten, with two new authors added.

We have fixed some of the original results and now we:
-Show how some fundamental theorem

Steve Flammia Jul 21 2017 13:43 UTC

Actually, there is even earlier work that shows this result. In [arXiv:1109.6887][1], Magesan, Gambetta, and Emerson showed that for any Pauli channel the diamond distance to the identity is equal to the trace distance between the associated Choi states. They prefer to phrase their results in terms

Stefano Pirandola Jul 21 2017 09:43 UTC

This is very interesting. In my reading list!

gae Jul 21 2017 09:00 UTC

In relation with the discussion at page 21 of this paper. Consider depolarizing channels (including the trivial case of the identity channel) which are teleportation covariant as in the definition Eq. (9) of [Nature Communications 8, 15043 (2017)]. The diamond norm b

Chris Ferrie Jul 18 2017 02:32 UTC

Since arXiv now supports supplementary material, we did not host the source externally. The easiest way to view the code is using

By the way, if you are having difficulty navigating

Ashley Jul 14 2017 20:02 UTC

Thanks! Yes, I think a generalisation of this form ought to work, though I didn't work out the details.

Vlad Gheorghiu Jul 14 2017 18:11 UTC

Nice result! It looks like the technique is easily generalizable to qudits, isn't it, by replacing the bell states with $|b_{ij}\rangle = (X^iZ^j \otimes I) \frac{1}{\sqrt{D}}\sum_{k=0}^{D-1}|kk>$, where $X|i\rangle=|i\oplus1>$ and $Z|i\rangle=\omega^i|i\rangle$? Fo course $\mathbb{F}_2^n$ will beco

Blake Stacey Jul 11 2017 16:27 UTC

Eight hundred forty-four!

C. Jess Riedel Jul 04 2017 21:26 UTC

Even if we kickstart evolution with bacteria, the amount of time until we are capable of von Neumann probes is almost certainly too small for this to be relevant. See for instance [Armstrong & Sandberg]( It

Noon van der Silk Jun 29 2017 23:51 UTC

Wow, from one-way QC to AI! :)

xecehim Jun 27 2017 15:03 UTC

It has been [published][1]


Kenneth Goodenough Jun 21 2017 12:48 UTC

Ah yes I see, thank you for the clarification!

Stefano Pirandola Jun 20 2017 13:26 UTC

Hi Kenneth, more precisely that plot is for a particular "Pauli-damping" channel, i.e., a qubit channel that is decomposable into a Pauli channel (1) and an amplitude damping channel (2). This "Pauli-damping" channel can be simulated by performing noisy teleportation over a resource state that corre

Kenneth Goodenough Jun 20 2017 12:47 UTC

Interesting work! I was wondering, how do the new upper bounds for the amplitude-damping channel in Fig. 2 compare to previous bounds?

Barbara Terhal Jun 20 2017 07:25 UTC

It would be good if this conflict on assigning priority and credit is peacefully resolved by the parties involved (i have no opinions on the matter).

Stefano Pirandola Jun 15 2017 05:32 UTC

The secret-key capacity of the pure-loss channel -log(1-t) was proven in [9], not in the follow-up work [13] (which appeared 4 months later). Ref. [13] found that this capacity is also a strong converse bound, which is Eq. (1) here. Same story for Eq. (4) that was proven in [9], not in [13]. Again t

Chris Ferrie Jun 09 2017 10:06 UTC

I have posted an open review of this paper here:

Eddie Smolansky May 26 2017 05:23 UTC

Updated summary [here](

# How they made the dataset
- collect youtube videos
- automated filtering with yolo and landmark detection projects
- crowd source final filtering (AMT - give 50 face images to turks and ask which don't belong)
- quality control through s

Felix Leditzky May 24 2017 20:43 UTC

Yes, that's right, thanks!

For (5), you use the Cauchy-Schwarz inequality $\left| \operatorname{tr}(X^\dagger Y) \right| \leq \sqrt{\operatorname{tr}(X^\dagger X)} \sqrt{\operatorname{tr}(Y^\dagger Y)}$ for the Hilbert-Schmidt inner product $\langle X,Y\rangle := \operatorname{tr}(X^\dagger Y)$ wi

Michael Tolan May 24 2017 20:27 UTC

Just reading over Eq (5) on P5 concerning the diamond norm.

Should the last $\sigma_1$ on the 4th line be replaced with a $\sigma_2$? I think I can see how the proof is working but not entirely certain.

Noon van der Silk May 23 2017 11:15 UTC

I think this thread has reached it's end.

I've locked further comments, and I hope that the quantum computing community can thoughtfully find an approach to language that is inclusive to all and recognises the diverse background of all researchers, current and future.

I direct your attention t

Varun Narasimhachar May 23 2017 02:14 UTC

While I would never want to antagonize my peers or to allow myself to assume they were acting irrationally, I do share your concerns to an extent. I worry about the association of social justice and inclusivity with linguistic engineering, virtual lynching, censorship, etc. (the latter phenomena sta

Aram Harrow May 23 2017 01:30 UTC

I think you are just complaining about issues that arise from living with other people in the same society. If you disagree with their values, well, then some of them might have a negative opinion about you. If you express yourself in an aggressive way, and use words like "lynch" to mean having pe

Steve Flammia May 23 2017 01:04 UTC

I agree with Noon that the discussion is becoming largely off topic for SciRate, but that it might still be of interest to the community to discuss this. I invite people to post thoughtful and respectful comments over at [my earlier Quantum Pontiff post][1]. Further comments here on SciRate will be

Noon van der Silk May 23 2017 00:59 UTC

I've moderated a few comments on this post because I believe it has gone past useful discussion, and I'll continue to remove comments that I believe don't add anything of substantial value.


Aram Harrow May 22 2017 23:13 UTC

The problem with your argument is that no one is forcing anyone to say anything, or banning anything.

If the terms really were offensive or exclusionary or had other bad side effects, then it's reasonable to discuss as a community whether to keep them, and possibly decide to stop using them. Ther

stan May 22 2017 22:53 UTC

Fair enough. At the end of the day I think most of us are concerned with the strength of the result not the particular language used to describe it.

VeteranVandal May 22 2017 22:41 UTC

But how obvious is ancilla? To me it is not even remotely obvious (nor clear as a term, but as the literature used it so much, I see such word in much the same way as I see auxiliary, in fact - now if you want to take offense with auxiliary, what can I say? I won't invent words just to please you).