  A digital currency is money in a digital form. In this model, maintaining
integrity of the supply is a core concern, therefore protections against
double-spending are often at the heart of a secure digital money scheme.
Quantum money exploits the quantum mechanical principle of no-cloning to enable
a currency that is immune to double spending. One of the challenges of the
scheme is that users require technology that is currently out of reach. Here,
we propose a model for quantum currency, which alleviates the need for quantum
wallets by delegating quantum storage and processing to an intermediary that we
call a "quantum vault". We develop the basic building blocks of this
quantum-enabled digital currency and discuss its benefits and challenges.
