Quantum Secret Sharing with Classical and Quantum Shares

TL;DR

This paper explores quantum secret sharing involving both classical and quantum shares, establishing feasibility conditions, minimum share sizes, and optimal schemes using quantum information theory and classical secret sharing techniques.

Contribution

It introduces the first comprehensive analysis of quantum secret sharing with mixed classical and quantum shares, including feasibility conditions and minimal share size characterizations.

Findings

Quantum secret sharing with classical and quantum shares is feasible if any two qualified sets share a quantum share.

Sharing one qubit secret requires each classical share to be at least 2 bits and each quantum share at least 1 qubit.

The paper characterizes minimal share sizes for schemes with up to 2 classical and 2 quantum shares.

Abstract

In quantum secret sharing, a quantum secret state is mapped to multiple shares such that shares from qualified sets can recover the secret state and shares from other forbidden sets reveal nothing about the secret state; we study the setting where there are both classical shares and quantum shares. We show that the quantum secret sharing problem with both classical and quantum shares is feasible if and only if any two qualified sets have some quantum share in common. Next, for threshold quantum secret sharing where there are $N_1$ classical shares, $N_2$ quantum shares and qualified sets consist of any $K_1$ (or more) classical shares and any $K_2 > N_2/2$ (or more) quantum shares, we show that to share $1$ qubit secret, each classical share needs to be at least $2$ bits and each quantum share needs to be at least $1$ qubit. Finally, we characterize the minimum share sizes for quantum secret sharing with at most $2$ classical shares and at most $2$ quantum shares. The converse proofs rely on quantum information inequalities and the achievable schemes use classical secret sharing, (encrypted) quantum secret sharing with only quantum shares, superdense coding, treating quantum digits as classical digits, and their various combinations.