Ewin Tang

collaborators

8 papers

quant-ph2026

Pretty good shadow tomography

Sabee Grewal, Angelos Pelecanos, Jack Spilecki +2

We give a shadow tomography algorithm that uses $O (lo g (m) lo g (m / δ) / ε^{2})$ copies of the input state. Specifically, given a quantum state $ρ$ and observables $O_1,\ldot…

quant-ph2026

The Keyl-Werner algorithm is not optimal for spectrum estimation

Angelos Pelecanos, Jack Spilecki, Ewin Tang +1

We give an algorithm which, given $n = O (d^{2} \cdot (lo g lo g (d) / lo g (d))^{2})$ copies of $ρ$ , estimates the eigenvalues of $ρ$ to constant error in total variation distance. Thus, we…

quant-ph2026

Learning the structure of open quantum systems

Laura Lewis, Ewin Tang, John Wright

We design an algorithm for learning the coefficients of an $n$ -qubit constant-local Lindbladian to $ε$ error with $O (g d^{2} lo g (n) / ε^{2})$ total evolution time,…

quant-ph2025

Mixed state tomography reduces to pure state tomography

Angelos Pelecanos, Jack Spilecki, Ewin Tang +1

A longstanding belief in quantum tomography is that estimating a mixed state is far harder than estimating a pure state. This is borne out in the mathematics, where mixed state alg…

quant-ph2025

Conjugate queries can help

Ewin Tang, John Wright, Mark Zhandry

We give a natural problem over input quantum oracles $U$ which cannot be solved with exponentially many black-box queries to $U$ and $U^{†}$ , but which can be solved with const…

quant-ph2025

Are controlled unitaries helpful?

Ewin Tang, John Wright

Many quantum algorithms, to compute some property of a unitary $U$ , require access not just to $U$ , but to $c U$ , the unitary with a control qubit. We show that having access to $cU…

quant-ph2025

Amplitude amplification and estimation require inverses

Ewin Tang, John Wright

We prove that the generic quantum speedups for brute-force search and counting only hold when the process we apply them to can be efficiently inverted. The algorithms speeding up t…

quant-ph2025

Beating full state tomography for unentangled spectrum estimation

Angelos Pelecanos, Xinyu Tan, Ewin Tang +1

How many copies of a mixed state $ρ \in C^{d \times d}$ are needed to learn its spectrum? To date, the best known algorithms for spectrum estimation require as many copies…