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Paper 1
Universal Quantum Random Access Memory: A Data-Independent Unitary with a Commuting-Projector Hamiltonian
Leonardo Bohac
- Year
- 2025
- Journal
- arXiv preprint
- DOI
- arXiv:2512.12999
- arXiv
- 2512.12999
Quantum random access memory (QRAM) is a central primitive for coherent data access in quantum algorithms, yet it remains controversial in practice because the wall-clock cost of "one lookup" can hide routing depth, control overhead, and geometric constraints. We present a universal QRAM construction (U-QRAM) in which the database is a physical memory register that participates in the lookup unitary as quantum control. This yields a single fixed, data-independent lookup unitary on $A \otimes D \otimes M$ that is correct for all basis-encoded databases. Our first contribution is an explicit, exact Hamiltonian realization: U-QRAM equals a single time-independent evolution $U_{QRAM} = \exp(-iH_{tot})$ where $H_{tot}$ is a sum of mutually commuting projector terms, one per memory cell, and the construction avoids control-dependent phase ambiguities. Our second contribution is an architectural sharpening: under unary (one-hot, mode-addressed) encoding of the address, each cell term becomes uniform and 3-local, delineating the most direct path toward constant-latency interpretations. We keep claims conservative by separating latency from work and stating explicit hardware assumptions required for constant wall-clock queries.
Open paperPaper 2
Trotterless Simulation of Open Quantum Systems for NISQ Quantum Devices
Colin Burdine, Enrique P. Blair
- Year
- 2024
- Journal
- arXiv preprint
- DOI
- arXiv:2410.03854
- arXiv
- 2410.03854
The simulation of quantum systems is one of the flagship applications of near-term NISQ (noisy intermediate-scale quantum) computing devices. Efficiently simulating the rich, non-unitary dynamics of open quantum systems remains challenging on NISQ hardware. Current simulation methods for open quantum systems employ time-stepped Trotter product formulas ("Trotterization") which can scale poorly with respect to the simulation time and system dimension. Here, we propose a new simulation method based on the derivation of a Kraus operator series representation of the system. We identify a class of open quantum systems for which this method produces circuits of time-independent depth, which may serve as a desirable alternative to Trotterization, especially on NISQ devices.
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