I am Yingkai Ouyang, and below are some videos and cartoons highlighting a featured selection of my research portfolio.


2020 IEEE ISIT: Linear programming bounds for quantum amplitude damping codes (15 min)

Authors: Yingkai Ouyang, Ching-Yi Lai

Abstract: Given that approximate quantum error-correcting (AQEC) codes have a potentially better performance than perfect quantum error correction codes, it is pertinent to quantify their performance. While quantum weight enumerators establish some of the best upper bounds on the minimum distance of quantum error-correcting codes, these bounds do not directly apply to AQEC codes. Herein, we introduce quantum weight enumerators for amplitude damping (AD) errors and work within the framework of approximate quantum error correction. In particular, we introduce an auxiliary exact weight enumerator that is intrinsic to a code space and moreover, we establish a linear relationship between the quantum weight enumerators for AD errors and this auxiliary exact weight enumerator. This allows us to establish a linear program that is infeasible only when AQEC AD codes with corresponding parameters do not exist. To illustrate our linear program, we numerically rule out the existence of three-qubit AD codes that are capable of correcting an arbitrary AD error.

Quantum simulation. Featured on Quantum Perspective

2020 QCTIP: Compilation by stochastic Hamiltonian sparsification (20 min)

Quantum 4, 235, 2020/2/17

Authors: Yingkai Ouyang, David R White, Earl T Campbell

Simulation of quantum chemistry is expected to be a principal application of quantum computing. In quantum simulation, a complicated Hamiltonian describing the dynamics of a quantum system is decomposed into its constituent terms, where the effect of each term during time-evolution is individually computed. For many physical systems, the Hamiltonian has a large number of terms, constraining the scalability of established simulation methods. To address this limitation we introduce a new scheme that approximates the actual Hamiltonian with a sparser Hamiltonian containing fewer terms. By stochastically sparsifying weaker Hamiltonian terms, we benefit from a quadratic suppression of errors relative to deterministic approaches. Tuning the sparsity of our approximate Hamiltonians allows our scheme to interpolate and outperform two recent random compilers.

Robust quantum metrology with explicit symmetric states (3 min)

Abstract: Quantum metrology is a promising practical use case for quantum technologies, where physical quantities can be measured with unprecedented precision. In lieu of quantum error correction procedures, near term quantum devices are expected to be noisy, and we have to make do with noisy probe states. With carefully chosen symmetric probe states inspired by the quantum error correction capabilities of certain symmetric codes, we prove that quantum metrology can exhibit an advantage over classical metrology, even after the probe states are corrupted by a constant number of erasure and dephasing errors. These probe states prove useful for robust metrology not only in the NISQ regime, but also in the asymptotic setting where they achieve Heisenberg scaling. This brings us closer towards making robust quantum metrology a technological reality.


How can we make bespoke quantum error correction codes on a quantum bus?

The Hamiltonian of a quantum bus is simply a sum of independent bosonic oscillators. By designing constant-excitation bosonic quantum codes that can correct loss errors, we can have a robust quantum bus. See my publication in IEEE Transactions on Information Theory.