Questions tagged [nonlocal-games]

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Can Alice and Bob convince the cops that they don't share any entanglement?

Suppose Alice and Bob are arrested for killing Eve, and are taken to two different interrogation rooms. The police quiz Alice and separately Bob, asking them a bunch of different questions along the ...
Mark Spinelli's user avatar
1 vote
0 answers
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Magic square operator's measurement product

In the talk by Andrea Coladangelo (link) at 29:30, he claims that if $X_1X_2X_3 = I$, such that the operators commute. Then, the product of the measurement results on an EPR pair of the same dimension ...
Zee's user avatar
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2 votes
1 answer
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Why are randomized strategies convex mixtures of deterministic ones?

I am looking for a proof of this fact regarding randomized strategies of the CHSH game: "... allowing randomized strategies can not help them to get a better success probability. This is because ...
NotaChoice's user avatar
0 votes
0 answers
33 views

Parallel repetition to amplify the gap for nonlocal games

Suppose for an one-round nonlocal game $G$ with question size $n$, answer size $2$ (i.e the answer is yes or no), a verifier and two provers Alice and Bob sharing $\text{Poly}(n)$ entangled-qubits. If ...
qmww987's user avatar
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2 votes
0 answers
28 views

Spreading entanglement over multiple systems

Question: imagine that Alice and Bob share, say, one ebit $\lvert\Phi_+\rangle_\text{AB}$, and that they are only able to carry out local operations and classical communication. Is there an algorithm ...
Franklin Pezzuti Dyer's user avatar
7 votes
1 answer
511 views

Worst Bell inequality violation with non-maximally entangled state?

I'm familiar with CHSH game and the strategy that allows Alice and Bob to succeed with a probability of $$\frac{1+\tfrac{1}{\sqrt 2}}{2}\approx 85\%$$ if they share a maximally entangled state such as ...
Franklin Pezzuti Dyer's user avatar
-1 votes
1 answer
65 views

In the CHSH game, why do $a,b$ need to be the same unless $x=y=1$?

In this lecture, in the CHSH game section, it is claimed that a and b must be the same unless x and y are both 1. Can someone explain why? I see it the other way around.
random person's user avatar
2 votes
2 answers
356 views

Why is an X gate a quantum coin flip?

I am reading this page of Qiskit's textbook. I noticed that it extends coin games to quantum computers by defining an $X$ gate to be a classical coin flip. However, I do not understand this. For ...
Loic Stoic's user avatar
1 vote
1 answer
84 views

XOR game quantum strategy expected payoff?

I am reading Thomas Vidick, Quantum multiplayer games, testing and rigidity. On top of p.4, $$\text{E}[a\cdot b] = \sum_{i,j\in \{0,1\}}(-1)^{i+j}\text{Pr}\big((a,b)=(i,j)\big)$$ I do not understand ...
Hans's user avatar
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2 votes
1 answer
113 views

Local operation to change the maximally mixed 2 qubit state to $\frac{1}{2}(|01\rangle \langle01|+|10\rangle \langle10|)$?

A paper I read talked about local interactions on only a single subsystem, leaving the state of that subsystem invariant, and the observation of this requiring the whole state. Here is the paper Now ...
GaussStrife's user avatar
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What is the quantum strategy required to win the Magic Squares game

This question is about the Magic Squares game. Links here, here and link here in which two players try to win a game. It's a cooperative game - either the team wins or the team loses. It is claimed ...
Anna Naden's user avatar
2 votes
2 answers
519 views

How can one show that Alice's and Bob's answers agree at the intersection cells of Mermin-Peres' "magic square"?

This question is along the lines of Problems in understanding the solution for "Mermin–Peres Magic Square Game" How can one show that Alice's and Bob's answers agree at the intersection ...
KCS's user avatar
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5 votes
0 answers
69 views

Who first studied nonlocal games with probabilistic predicate?

For some background, a nonlocal game consists of questions $x,y\in X,Y$ and answers $a,b \in A,B$; the pair of questions $x,y$ is asked with probability $\mu(x,y)$, and a referee accepts the pair of ...
Mateus Araújo's user avatar
1 vote
0 answers
109 views

Modified CHSH game - Does entanglement help?

I'm thinking about a modified version of the CHSH game and I'm trying to convince myself that in this case, entanglement cannot be used to gain an advantage or else it would imply signalling is ...
Stephen Diadamo's user avatar
3 votes
1 answer
145 views

How are Franson Interferometers used to prove security in Photonic QKD Experiments?

I am currently reading this paper about Quantum Key Distribution Protocols which use Franson Interferometers to secure against eavesdroppers. I am having trouble understanding how the interferometers ...
Dunbar Birnie's user avatar
4 votes
2 answers
256 views

How does a classical computer simulate nonclassical correlations?

This may be a dumb question, if so please forgive me, it is late at night. I have learned that a classical computer can simulate a quantum computer in exponential time and space, but classical ...
SescoMath's user avatar
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1 answer
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Problems in understanding the solution for "Mermin–Peres Magic Square Game"

I am referring to the article Advanced Topics in Quantum Information Theory exercise 4 and to the MS Quantum Kata MS-Quantum-Kata which describes a solution for the Mermin–Peres Magic Square Game. I ...
mbuchberger1967's user avatar
3 votes
1 answer
203 views

MS Quantum Katas - Measurements Task 2.3 - problems in understanding the solution

I am referring to the MS Quantum Katas, Measurements, 2.3 Peres/Wooters game I have big problems to understand the solution. The task is defined as: --begin Input: A qubit which is guaranteed to be ...
mbuchberger1967's user avatar
5 votes
1 answer
311 views

Is Connes' Embedding Problem akin to the word problem for finitely presented groups?

The complexity class $\mathrm{MIP^*}$ includes the set of languages that can be efficiently verified by a classical, polynomially-bounded verifier, engaging with two quantum provers that can share (...
Mark Spinelli's user avatar
2 votes
2 answers
172 views

Using Qiskit with Blender

I want to use Blender and Blender Python Scripts working with Qiskit. (want to make 3D creations) (www.blender.org) How can I do this ? (because when I try to install Qiskit inside Blender Python, it ...
Alain Lioret's user avatar
6 votes
1 answer
223 views

Why is $P(1,2)_{\text{same}} = \frac{1}{4}$ and not $\frac{1}{2}$ in Preskill's Bell experiment?

Context: Three coins on the table. Each is either heads or tails. You can uncover any one of the three coins, revealing whether it is heads or tails but then you choose two the other two coins ...
Sanchayan Dutta's user avatar
9 votes
2 answers
1k views

Optimal strategy to a quantum state game

Consider the following game: I flip a fair coin, and depending on the outcome (either heads/tails), I'll give you one of the following states: $$|0\rangle \text{ or } \cos(x)|0\rangle + \sin(x)|1\...
jjbid's user avatar
  • 91
5 votes
1 answer
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How can quantum computing win 97% of times in coin flipping experiment?

I'm new to this field of science. I'm curious about how quantum computing can win 97% of times in a coin flipping experiment? Refer this link: Ted Talk by Shohini Ghose To give an idea about how ...
Saddam Pojee's user avatar
9 votes
3 answers
2k views

Proof of optimality for CHSH game classical strategy

I'm aware that the optimality of the quantum strategy for the CHSH game is given by Tsirelson's bound, but presentations all skip over the (admittedly much less interesting) proof of the classical ...
ahelwer's user avatar
  • 4,078
3 votes
2 answers
320 views

How could a quantum computer perform nimber arithmetic?

I am interested in combinatorial game theory & was doing some research on quantum combinatorial games. This lead me to wondering how a quantum computer might be able to perform nimber arithmetic (...
user820789's user avatar
  • 3,302
3 votes
1 answer
166 views

How are nonlocal games used in device-independent quantum cryptography?

As I understand it, device-independent quantum cryptography enables you to safely perform cryptographic operations without necessarily trusting the quantum device on which they are performed. Nonlocal ...
ahelwer's user avatar
  • 4,078
3 votes
0 answers
92 views

Photonic CHSH Games

How can a CHSH game be realized in a photonic circuit?
user820789's user avatar
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13 votes
3 answers
563 views

Are correlations stronger than those allowed by quantum mechanics possible?

We know how a quantum correlation setup can help us with a better probability of winning games like the CHSH. But what is the upper bound that physics can allow? Is it the quantum correlation setup? ...
Siddhant Singh's user avatar
4 votes
1 answer
141 views

Using XOR games to benchmark quantum computers

In an answer to a previous question, What exactly are Quantum XOR Games?, ahelwer states: One application of xor games is self-testing: when running algorithms on an untrusted quantum computer, you ...
user820789's user avatar
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7 votes
1 answer
352 views

In which paper was the CHSH game first presented?

The CHSH inequality was presented in the paper Proposed Experiment to Test Local Hidden-Variable Theories published in 1969 by J.F. Clauser, M.A. Horne, A. Shimony, and R.A. Holt. I'm interested in ...
ahelwer's user avatar
  • 4,078
5 votes
3 answers
313 views

Algorithm-based game project to introduce quantum computing

I am currently working on a quantum computing subject for my coding school, and I had some questions for you. My objective would be to introduce students to quantum computing with an algorithmic ...
F. Sabatié's user avatar
15 votes
1 answer
1k views

What exactly are Quantum XOR Games?

I have done some research & found a few different papers that discuss xor games (classic & quantum). I am curious if someone could give a concise introductory explanation as to what exactly ...
user820789's user avatar
  • 3,302
7 votes
1 answer
199 views

Has anyone analyzed multi-round nonlocal games?

The traditional definition of a nonlocal game is restricted to having two players and one round (e.g., here), but it is natural to consider a more general class of games that may have more than two ...
Evan Jenkins's user avatar