Practical applications of quantum computing depend on fault-tolerant devices that employ error correction. A promising quantum error-correcting code for large-scale quantum computing is the surface code. For this code, Fault-Tolerant Quantum Computing (FTQC) can be performed via lattice surgery, i.e. merging and splitting of encoded qubit patches on a 2D grid. Lattice surgery operations result in space-time patterns of activity that are defined in this work as access traces. This work demonstrates that the access traces reveal when, where, and how logical qubits interact. Leveraging this formulation, this work further introduces TraceQ, a tracebased reconstruction framework that is able to reconstruct the quantum circuit dataflow just by observing the patch activity at each trace entry. The framework is supported by heuristics for handling inherent ambiguity in the traces, and demonstrates its effectiveness on a range of synthetic fault-tolerant quantum benchmarks. The access traces can have applications in a wide range of scenarios, enabling analysis and profiling of execution of quantum programs and the hardware they run on. As one example use of TraceQ, this work investigates whether such traces can act as a side channel through which an observer can recover the circuit's structure and identify known subroutines in a larger program or even whole programs. The findings show that indeed the minimal access traces can be used to recover subroutines or even whole quantum programs with very high accuracy. Only a single trace per program execution is needed and the processing can be done fully offline. Along with the custom heuristics, advanced subgraph matching algorithms used in this work enable a high rate of locating the subroutines while executing in minimal time.

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We present the first architecture for a trusted execution environment for quantum computers. In the architecture, to protect the user's circuits, they are obfuscated with decoy control pulses added during circuit transpilation by the user. The decoy pulses are removed, i.e. attenuated, by the trusted hardware inside the superconducting quantum computer's fridge before they reach the qubits. This preliminary work demonstrates that protection from possibly malicious cloud providers is feasible with minimal hardware cost.

Cloud computing providers today offer access to a variety of devices, which users can rent and access remotely in a shared setting. Among these devices are SmartSSDs, which are solid-state disks (SSD) augmented with an FPGA, enabling users to instantiate custom circuits within the FPGA, including potentially malicious circuits for power and temperature measurement. Normally, cloud users have no remote access to power and temperature data, but with SmartSSDs they could abuse the FPGA component to instantiate circuits to learn this information. Additionally, custom power waster circuits can be instantiated within the FPGA. This paper shows for the first time that by leveraging ring oscillator sensors and power wasters, numerous covert-channels in FPGA-enabled SmartSSDs could be used to transmit information. This work presents two channels in single-tenant setting (SmartSSD is used by one user at a time) and two channels in multi-tenant setting (FPGA and SSD inside SmartSSD is shared by different users). The presented covert channels can reach close to 100% accuracy. Meanwhile, bandwidth of the channels can be easily scaled by cloud users renting more SmartSSDs as the bandwidth of the covert channels is proportional to number of SmartSSD used.