Insights from the Quantum Era - October 2024

Classically estimating observables of noiseless quantum circuits

“Pauli-cutting” methods for simulation of quantum protocols are ramping up in prominence. After results showing the simulability of general noisy circuits a couple of months ago, now a new set of authors demonstrates how noiseless circuits on a broad class of protocols can also be simulated classically (with even better scaling!). While the methods are not applicable to all protocols - including error-corrected protocols or analog simulations - these results further help constrain the domain of applicability of quantum computing.

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Many-hypercube codes: High-rate quantum error-correcting codes for high-performance fault-tolerant quantum computing

Non-geometric codes are crucial for the encoding of logical qubits with high-rates, i.e. so that scaling the code size for better correction does not leave us with too few logical qubits. High-rate codes include quantum low-density parity-check codes, but these bring a trade-off in parallelizability and general overhead of operations. In this work, a new class of hypercube codes is introduced that promises to provide both high-rates and parallelizable logical operations, shaping a promising direction for fault-tolerance. The hypercube structure favored by these systems is particularly exciting given the compilation constraints of atomic qubit shuttling architectures

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Rapid initial state preparation for the quantum simulation of strongly correlated molecules

Although quantum chemistry is accepted as a key application sector for quantum computing, protocols for this are highly resource intensive. One of the issues is the capacity of preparing reliably states whose overlap modulus with the true ground state of a chemical system is high. This work considers strategies to address this challenge via faster preparation of approximate states and more efficient filtering of the prepared state. The authors achieve lower demands of Toffoli gate counts and test their results via estimates on the FeMo cofactor paradigmatic molecular system.

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Magic state cultivation: growing T states as cheap as CNOT gates

Magic state distillation is a demanding protocol necessary for generating T-states needed for universal quantum computation with logical qubits. Thus, counting T-states has been, so far, the key way of evaluating how demanding a fault-tolerant protocol can be. In this work, the authors propose a new methodology to prepare good T-states dubbed “Magic State Cultivation”. The Cultivation method is more efficient than the precursor Distillation strategies, requiring an order of magnitude less in qubit-rounds to achieve state-of-the art error rates. This result is groundbreaking, and while it does not change the resource needs of standard algorithms like Schor’s factorization or quantum phase estimation, it does strongly relax the hardware requirements for what a utility-scale quantum computer may need to perform.

This is one of 2024’s most noteworthy results.

Read here on arXiv