Quantum corrections and exchange

Bernard De Wit A, J. SMITH

Donovan L. Buterakos, Robert E. Throckmorton, S. Das Sarma

We present a scheme for correcting for crosstalk- and noise-induced errors in exchange-coupled singlet-triplet semiconductor double quantum dot qubits. While exchange coupling allows the coupling strength to be controlled independently of the intraqubit exchange couplings, there is also the problem of leakage, which must be addressed. We show that, if a large magnetic field difference is present between the two qubits, leakage is suppressed. We then develop pulse sequences that correct for crosstalk- and noise-induced errors and present parameters describing them for the 24 Clifford gates. We determine the infidelity for both the uncorrected and corrected gates as a function of the error-inducing terms and show that our corrected pulse sequences reduce the error by several orders of magnitude.

Lawrence Roy, Jiayu Xu

A Password-Authenticated Key Exchange (PAKE) protocol allows two parties to agree upon a cryptographic key, when the only information shared in advance is a low-entropy password. The standard security notion for PAKE (Canetti et al., Eurocrypt 2005) is in the Universally Composable (UC) framework. We show that unlike most UC security notions, UC PAKE does not imply correctness. While Canetti et al. has briefly noticed this issue, we present the first comprehensive study of correctness in UC PAKE: We show that TrivialPAKE, a no-message protocol that does not satisfy correctness, is a UC PAKE; We propose nine approaches to guaranteeing correctness in the UC security notion of PAKE, and show that seven of them are equivalent, whereas the other two are unachievable; We prove that a direct solution, namely changing the UC PAKE functionality to incorporate correctness, is impossible; Finally, we show how to naturally incorporate correctness by changing the model—we view PAKE as a three-party protocol, with the man-in-the-middle adversary as the third party. In this way, we hope to shed some light on the very nature of UC-security in the man-in-the-middle setting.

Martin Bojowald A

Mary Beth Ruskai

In many physically realistic models of quantum computation, Pauli exchange interactions cause a special type of two-qubit errors, called exchange errors, to occur as a first order effect of couplings within the computer. We discuss the physical mechanisms behind exchange errors and codes designed to explicitly deal with them.

Rajendra Kumar Bera