The quantum Fisher information (QFI) sets a fundamental bound on the attainable precision when estimating multiple parameters simultaneously. Incompatibility among the individually optimal measurements can, in some cases, imply that the precision limit set by the QFI is not attainable. In certain special cases, includi...
Lorcán O. Conlon, Laura Shou, V. Vijendran et al.· 0 citations
Experimental tests of shallow-circuit quantum advantage require explicit classical bounds at finite circuit sizes. We refine the finite-size classical soundness bound of Aasnaess's graph-distributed construction to depend linearly on the number of players. Combined with standard disjoint-player repetition, this gives a...
Recent work established that, for independent erasures, storing $K$ logical qubits for $S$ time steps with error at most $\varepsilon$ requires a spacetime cost of $\Omega(S(K+\log(S/\varepsilon)))$. A matching construction was also given, but assumes ideal error correction. Here we show that the same scaling can be ac...
Kishor Bharti, Tobias Haug, Derek Khu et al.· 0 citations
We study a family of quantum subsystem codes defined on rectangular coordinate grids of any dimension, with even side lengths of at least four. The directly measured operators act along coordinate lines. For every member of the family, we derive the number of protected logical qubits and prove its dressed distance with...
Kishor Bharti, Tobias Haug, Run-Zhou Tao et al.· 0 citations
The most general strategy for estimating parameters of a quantum channel is to probe the channel many times sequentially with the help of coherent ancillary systems. However, finding the strategy that minimizes the mean-squared error (MSE) is a notoriously hard problem, requiring optimization over the initial probe sta...
Andrew Tanggara, Lorcán O. Conlon, Alexey V. Gorshkov et al.· 0 citations
Syndrome-measurement timing is usually treated as a fixed clock cycle of a quantum error-correcting code. For quantum memories, however, the inter-round interval is itself an optimizable control parameter: measuring too rarely allows idling errors to accumulate, whereas measuring too often introduces measurement-induce...
Non-Clifford gates are essential for universal quantum computation, yet implementing them fault-tolerantly remains a central challenge for stabilizer codes. Here, we show how a syndrome degree of freedom can mediate a logical non-Clifford gate. Releasing one stabilizer check makes an additional logical qubit available...
Kishor Bharti, Tobias Haug, Andrew Tanggara· 0 citations
This work establishes fundamental limits on the resources required for quantum fault tolerance, and gives a positive-rate CSS code construction that attains the memory bound, and identifies sufficient conditions under which the same scaling extends from quantum memory to fault-tolerant circuit implementations.
Kishor Bharti, Tobias Haug, Andrew Tanggara· 1 citation
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