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We consider a quantum system continuously monitored in time which in turn is coupled to an arbitrary dissipative classical system (diagonal reduced density matrix). The quantum and classical dynamics can modify each other, being described…

Quantum Physics · Physics 2017-09-26 Adrián A. Budini

Understanding the dynamics of large quantum systems is hindered by the curse of dimensionality. Statistical learning offers new possibilities in this regime by neural-network protocols and classical shadows, while both methods have…

Quantum Physics · Physics 2023-08-23 Yuxuan Du , Yibo Yang , Tongliang Liu , Zhouchen Lin , Bernard Ghanem , Dacheng Tao

We develop classical simulation algorithms for adaptive quantum circuits that produce states with low levels of ``magic'' (i.e., non-stabilizerness). These algorithms are particularly well-suited to circuits with high rates of Pauli…

Quantum Physics · Physics 2026-05-22 Kemal Aziz , Haining Pan , Michael J. Gullans , J. H. Pixley

Many hybrid quantum-classical algorithms for the application of ground state energy estimation in quantum chemistry involve estimating the expectation value of a molecular Hamiltonian with respect to a quantum state through measurements on…

Local random circuits scramble efficiently and accordingly have a range of applications in quantum information and quantum dynamics. With a global $U(1)$ charge however, the scrambling ability is reduced; for example, such random circuits…

Statistical Mechanics · Physics 2025-04-23 Sumner N. Hearth , Michael O. Flynn , Anushya Chandran , Chris R. Laumann

We introduce a method to enforce some symmetries starting from a trial wave-function prepared on quantum computers that might not respect these symmetries. The technique eliminates the necessity for performing the projection on the quantum…

Quantum Physics · Physics 2023-11-09 Edgar Andres Ruiz Guzman , Denis Lacroix

We prove that estimating the ground state energy of a translationally-invariant, nearest-neighbour Hamiltonian on a 1D spin chain is QMAEXP-complete, even for systems of low local dimension (roughly 40). This is an improvement over the best…

Quantum Physics · Physics 2017-11-15 Johannes Bausch , Toby Cubitt , Maris Ozols

The performance of computational methods for many-body physics and chemistry is strongly dependent on the choice of basis used to cast the problem; hence, the search for better bases and similarity transformations is important for progress…

Out-of-Time-Order Correlators (OTOCs) quantify quantum information scrambling, but their connection to localized phase-space structures, such as chemical transition states, requires formal development. We derive a leading-order…

Quantum Physics · Physics 2026-04-15 Stephen Wiggins

Simulating noiseless quantum dynamics classically faces a fundamental dilemma: tensor-network methods become inefficient as entanglement saturates, while Pauli-truncation approaches typically rely on noise or randomness. To close the gap,…

Quantum Physics · Physics 2026-01-23 Jue Xu , Chu Zhao , Xiangran Zhang , Shuchen Zhu , Qi Zhao

Starting with the generally well accepted opinion that quantizing an arbitrary Hamiltonian system involves picking out some additional structure on the classical phase space (the {\sl shadow} of quantum mechanics in the classical theory),…

Quantum Physics · Physics 2009-10-30 J. R. Klauder , P. Maraner

Classical shadows constitute a protocol to estimate the expectation values of a collection of M observables acting on O(1) qubits of an unknown n-qubit state with a number of measurements that is independent of n and that grows only…

Quantum Physics · Physics 2024-10-03 Giacomo De Palma , Tristan Klein , Davide Pastorello

Quantum state tomography (QST) remains the prevailing method for benchmarking and verifying quantum devices; however, its application to large quantum systems is rendered impractical due to the exponential growth in both the required number…

Quantum Physics · Physics 2025-01-10 Zhen Qin , Joseph M. Lukens , Brian T. Kirby , Zhihui Zhu

We introduce the problem of *shadow tomography*: given an unknown $D$-dimensional quantum mixed state $\rho$, as well as known two-outcome measurements $E_{1},\ldots,E_{M}$, estimate the probability that $E_{i}$ accepts $\rho$, to within…

Quantum Physics · Physics 2018-11-14 Scott Aaronson

Enormous activity in the Quantum Computing area has resulted in considering them to solve different difficult problems, including those of applied nature, together with classical computers. An attempt is made in this work to nail down a…

The difficulty of simulating quantum dynamics depends on the norm of the Hamiltonian. When the Hamiltonian varies with time, the simulation complexity should only depend on this quantity instantaneously. We develop quantum simulation…

Quantum Physics · Physics 2020-04-21 Dominic W. Berry , Andrew M. Childs , Yuan Su , Xin Wang , Nathan Wiebe

The development of emerging technologies in quantum optics demands accurate models that faithfully capture genuine quantum effects. Mature semiclassical approaches reach their limits when confronted with quantized electromagnetic fields,…

Classical entanglement is a powerful tool which provides a neat numerical estimate for the study of classical correlations. Its experimental investigation, however, has been limited to special cases. Here, we demonstrate that the…

Optics · Physics 2017-05-24 E. Roccia , I. Gianani , L. Mancino , M. Sbroscia , I. Miatka , F. Somma , M. Barbieri

Simulating the dynamics of complex quantum systems is a central application of quantum devices. Here, we propose leveraging the power of measurements to simulate short-time quantum dynamics of physically prepared quantum states in classical…

Quantum Physics · Physics 2025-07-02 Paul K. Faehrmann , Jens Eisert , Maria Kieferova , Richard Kueng

We introduce a new family of quantum circuits for which the scrambling of a subspace of non-local operators is classically simulable. We call these circuits `super-Clifford circuits', since the Heisenberg time evolution of these operators…

Quantum Physics · Physics 2020-07-22 Mike Blake , Noah Linden