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Single-Shot Error Correction at Optimal Spacetime Cost
Kishor Bharti, Tobias Haug, Derek Khu +1
Recent work established that, for independent erasures, storing logical qubits for time steps with error at most requires a spacetime cost of $Ω(S(K+\log(S/\v…
Pricing of graph-based quantum portfolios from first principles
Daniel J. Spencer, Bin Cheng, Dinh-Long Vu +3
A central topic in economics and finance is the valuation of strategic games and bets, of investments providing uncertain future cashflows, and of other asset-like structures and c…
High-Rate Quantum Codes with Proven Distance and Low-Weight Measurements
Kishor Bharti, Tobias Haug, Runzhou Tao +1
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…
Function-like pseudorandom unitaries generate pseudorandom quantum processes
Zitai Xu, Rahul Arvind, Kishor Bharti +5
Haar-random unitaries provide a canonical model of generic random quantum evolution, but they typically have exponential description and circuit complexity. Although pseudorandom u…
Beyond IP = PSPACE and QIP = PSPACE: Interactive Proofs in Arbitrary Physical Theories
Kishor Bharti
The equalities IP = PSPACE and QIP = PSPACE, the latter achievable with three messages, raise a basic question: how much of an interactive proof's power comes from the underlying p…
Experimentally Testable Quantum Advantage in Shallow Circuits
Kishor Bharti, Adán Cabello
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…
Deciding the Attainability of the Multiparameter Quantum Fisher Information is NP-Hard
Lorcan O. Conlon, Laura Shou, V Vijendran +7
The quantum Fisher information (QFI) sets a fundamental bound on the attainable precision when estimating multiple parameters simultaneously. Incompatibility among the individually…
Optimal noisy sequential multiparameter quantum sensing
Andrew Tanggara, Lorcán O Conlon, Alexey V. Gorshkov +1
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, findi…
Syndrome measurements enable deterministic fault-tolerant gates
Kishor Bharti, Tobias Haug, Andrew Tanggara
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 syn…
Fault-tolerant quantum computation cannot be achieved with constant spacetime overhead
Kishor Bharti, Tobias Haug, Andrew Tanggara
The threshold theorem states that quantum computations can be made reliable below a physical error threshold, at the cost of additional physical qubits and circuit depth. Recent wo…
Exponential logical-error reduction in quantum memories via optimal syndrome-measurement timing
Tobias Haug, Kishor Bharti, Leandro Aolita
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 optim…
Two-copy nondistillability of Werner states: sharp partial-trace inequalities and finite-copy extensions
Kishor Bharti, Rishikesh Gajjala, Tobias Haug
We solve the two-copy distillability problem for Werner states in every local dimension. Our main matrix result is a sharp, dimension-free inequality: for every rank-at-most-two op…
An efficient Pauli decomposition algorithm for structured matrices
Daniel J. Spencer, Kishor Bharti, Alexey V. Gorshkov
Decomposing classical matrices into linear combinations of Pauli strings is a major bottleneck for end-to-end implementations of near-term quantum algorithms. In this work, we cons…
Quantum error correction and fault tolerance: A comprehensive tutorial
Daniel J. Spencer, Shubham P. Jain, Andrew Tanggara +4
Noise is one of the central obstacles to building useful quantum computers, and quantum error correction (QEC) provides the framework for protecting quantum information against it.…
Hierarchical quantum decoders
Nirupam Basak, Ankith Mohan, Andrew Tanggara +3
Decoders are a critical component of fault-tolerant quantum computing. They must identify errors based on syndrome measurements to correct quantum states. While finding the optimal…