<p>With the advancement of quantum computing, the block chain networks are now encountering new and critical threats to their security namely, asymmetric cryptographic protocols. To assess these technological-existential threats, this study aims to analyse how the volatility of major block chain-based cryptocurrency markets has been affected by developments in quantum computing. We employ a wide range of time-series econometric models such as GARCH-in-Mean, EGARCH, VAR and Impulse Response Function (IRF) techniques to undertake a detailed analysis of the daily dynamics of the leading quantum computing firms (Google, IBM, Microsoft and NVIDIA) and the biggest digital assets (Bitcoin, Ethereum, Litecoin, Monero and Zcash). Although at first glance the price behaviour of the two sectors appears to be independent from each other, high-level correlation statistics show that there are significant cross-sector relationships from the angle and depth of the price behaviour. The EGARCH model also indicates that the relationship between quantum equities and crypto isn't quite symmetrical: quantum stocks seem to be very sensitive to negative market shocks, while cryptocurrencies such as Ethereum and Zcash are particularly sensitive to positive technological advances. Moreover, VAR estimates validate that innovations like the Google announcement causes selective shocks in the cryptocurrencies that are privacy focused, such as Monero and Zcash. Thus, the finding of the study has a major implication which emphasize that major cryptocurrencies' volatility over time has a huge impact on quantum announcements. From a policy and practical view these findings suggest that regulators should incorporate the notion of quantum risk in current macro prudential stress testing regimes, especially in light of the ability of current practical quantum computing to break the traditional cryptography of block chain technology.</p>