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Electronic Colloquium on Computational Complexity

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All reports by Author Uma Girish:

TR23-148 | 3rd October 2023
Srinivasan Arunachalam, Uma Girish, Noam Lifshitz

One Clean Qubit Suffices for Quantum Communication Advantage

We study the one-clean-qubit model of quantum communication where one qubit is in a pure state and all other qubits are maximally mixed. We demonstrate a partial function that has a quantum protocol of cost $O(\log N)$ in this model, however, every interactive randomized protocol has cost $\Omega(\sqrt{N})$, settling a ... more >>>

TR23-107 | 20th July 2023
Uma Girish, Ran Raz, Wei Zhan

Quantum Logspace Computations are Verifiable

In this note, we observe that quantum logspace computations are verifiable by classical logspace algorithms, with unconditional security. More precisely, every language in BQL has an information-theoretically secure) streaming proof with a quantum logspace prover and a classical logspace verifier. The prover provides a polynomial-length proof that is streamed to ... more >>>

TR23-083 | 2nd June 2023
Srinivasan A, Uma Girish

Trade-offs between Entanglement and Communication

We study the advantages of quantum communication models over classical communication models that are equipped with a limited number of qubits of entanglement. In this direction, we give explicit partial functions on $n$ bits for which reducing the entanglement increases the classical communication complexity exponentially. Our separations are as follows. ... more >>>

TR22-043 | 2nd April 2022
Uma Girish, Kunal Mittal, Ran Raz, Wei Zhan

Polynomial Bounds On Parallel Repetition For All 3-Player Games With Binary Inputs

We prove that for every 3-player (3-prover) game $\mathcal G$ with value less than one, whose query distribution has the support $\mathcal S = \{(1,0,0), (0,1,0), (0,0,1)\}$ of hamming weight one vectors, the value of the $n$-fold parallel repetition $\mathcal G^{\otimes n}$ decays polynomially fast to zero; that is, there ... more >>>

TR22-039 | 14th March 2022
Uma Girish, Justin Holmgren, Kunal Mittal, Ran Raz, Wei Zhan

Parallel Repetition For All 3-Player Games Over Binary Alphabet

We prove that for every 3-player (3-prover) game, with binary questions and answers and value less than $1$, the value of the $n$-fold parallel repetition of the game decays polynomially fast to $0$. That is, for every such game, there exists a constant $c>0$, such that the value of the ... more >>>

TR21-101 | 13th July 2021
Uma Girish, Justin Holmgren, Kunal Mittal, Ran Raz, Wei Zhan

A Parallel Repetition Theorem for the GHZ Game: A Simpler Proof

Revisions: 1

We give a new proof of the fact that the parallel repetition of the (3-player) GHZ game reduces the value of the game to zero polynomially quickly. That is, we show that the value of the $n$-fold GHZ game is at most $n^{-\Omega(1)}$. This was first established by Holmgren and ... more >>>

TR21-087 | 22nd June 2021
Uma Girish, Ran Raz

Eliminating Intermediate Measurements using Pseudorandom Generators

Revisions: 1

We show that quantum algorithms of time T and space $S \ge \log T$ with intermediate measurements can be simulated by quantum algorithms of time $T\cdot \mathrm{poly}(S)$ and space $O(S\cdot \log T)$ without intermediate measurements. The best simulations prior to this work required either $\Omega(T)$ space (by the deferred measurement ... more >>>

TR21-046 | 22nd March 2021
Uma Girish, Avishay Tal, Kewen Wu

Fourier Growth of Parity Decision Trees

We prove that for every parity decision tree of depth $d$ on $n$ variables, the sum of absolute values of Fourier coefficients at level $\ell$ is at most $d^{\ell/2} \cdot O(\ell \cdot \log(n))^\ell$.
Our result is nearly tight for small values of $\ell$ and extends a previous Fourier bound ... more >>>

TR20-101 | 7th July 2020
Uma Girish, Ran Raz, Wei Zhan

Lower Bounds for XOR of Forrelations

The Forrelation problem, first introduced by Aaronson [AA10] and Aaronson and Ambainis [AA15], is a well studied computational problem in the context of separating quantum and classical computational models. Variants of this problem were used to give tight separations between quantum and classical query complexity [AA15]; the first separation between ... more >>>

TR20-087 | 8th June 2020
Uma Girish, Ran Raz, Wei Zhan

Quantum Logspace Algorithm for Powering Matrices with Bounded Norm

Revisions: 2

We give a quantum logspace algorithm for powering contraction matrices, that is, matrices with spectral norm at most 1. The algorithm gets as an input an arbitrary $n\times n$ contraction matrix $A$, and a parameter $T \leq poly(n)$ and outputs the entries of $A^T$, up to (arbitrary) polynomially small additive ... more >>>

TR19-152 | 6th November 2019
Uma Girish, Ran Raz, Avishay Tal

Quantum versus Randomized Communication Complexity, with Efficient Players

We study a new type of separation between quantum and classical communication complexity which is obtained using quantum protocols where all parties are efficient, in the sense that they can be implemented by small quantum circuits with oracle access to their inputs. More precisely, we give an explicit partial Boolean ... more >>>

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