Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Dissipative preparation of many-body states

Josias Langbehn

Published Jan 1, 2025• 0 citations
Publisher

Abstract

The controlled preparation of quantum many-body states is a central challenge for quantum technologies. While preparing target states coherently is possible in principle, it is often fragile and experimentally demanding. Dissipative state preparation, where engineered environments drive the system toward desired steady states, provides a complementary and powerful paradigm. This thesis explores dissipative methods for preparing complex many-body states along three distinct directions. First, we investigate the dissipative stabilization of injective matrix product states (MPS). Injective MPS are particularly well suited for dissipative preparation because they arise as ground states of frustration-free parent Hamiltonians, allowing for tailored jump operators to steer the system directly into the target state. We showcase the surprising result that such state preparation works even in the dilute limit where steering only acts on a single link. Moreover, we introduce a formalism for engineering additional coherent interactions, extending the set of accessible states. Second, and complementary to steering, we develop and analyze a universal cooling scheme capable of preparing ground states even in frustrated quantum systems. In contrast to steering methods, universal cooling can overcome the glass floor that forbids steering methods to prepare such frustrated ground states. A key insight here is that the presented cooling scheme is completely system-agnostic making it extremely robust. Finally, we pursue dressing of the system eigenstates by means of either classical drives or coherent interactions as a means to influence the action of dissipation on the system. Focusing first on time-dependent systems, we propose a generalized numerical implementation of non-adiabatic master equations suitable for the use of optimal control tools. Additionally, we investigate how the collective coupling between a spin ensemble and a cavity can steer the system into a spin-squeezed steady state. Together, these three avenues illustrate how tailored dissipative dynamics can extend the frontier of many-body state preparation, from stabilizing injective MPS to cooling complex frustrated systems and generating non-classical steady states in the dressed framework.

DOI
10.17169/refubium-52237

Related papers

Quantum technological applications using dissipative many-body dynamics

Meghana Raghunandan

Quantum systems cannot always be treated as isolated from their surroundings since this is an idealization which is not always true. Though theoretical analysis of open quantum systems poses great challenges as one needs to treat many-particle quantum systems as a whole, the system-environment interactions often lead to many interesting effects that are not observed in closed systems. The dissipation of a quantum system is not always a disadvantage and, in fact, if exploited properly in combination of coherent driving, one can steer the system into a desired state. This dissipation driven quantum state engineering technique finds its applications in novel technologies such as quantum computing, quantum simulation, and quantum metrology. In this thesis, we focus on the latter two, and show that using dissipative channels allows us to build quantum devices that have considerable advantages over their entirely coherent analogues. Simulation of many-body problems on a quantum simulator will unlock the potential to provide great insights into a large number of systems especially those that are computationally intractable or experimentally challenging. The two crucial steps towards the successful functioning of quantum simulation are the initialization of the quantum simulators i.e, preparing the system in a known initial state, and the Hamiltonian engineering. While there have been many experiments demonstrating the implementation of the Hamiltonian dynamics on the quantum simulator, work still needs to be done on the problem of preparing the simulator in a suitable quantum state. This is exactly our aim here and we propose a protocol to cool a given system into the ground state of a black-box spin Hamiltonian. The central idea is to use a dissipatively driven auxiliary spin to pull out the excitations in the system, eventually cooling it to its ground state. We show that already a single auxiliary spin is efficient in cooling the quantum simulator to a low-energy state of largely arbitrary Hamiltonians as the resources scale only polynomially with the system size. We also show that our scheme of sympathetic cooling is robust against additional sources of decoherence. The second part of the thesis deals with nanoscale quantum sensing using dissipative first order transition in the magnetization of a system of nitrogen-vacancy point defect centers in diamond. The sensitivity of a generic quantum sensor with non-interacting particles scales as the square root of the number of particles. Therefore, a sensor with large number of particles displays a better sensitivity. However, in the interest of nanoscale sensing, having a large number of particles implies that they are closely packed next to each other. At such high densities, the particles interact strongly with each other posing great challenges to the sensing process. Here, we show that these interactions can in fact be used to trigger a first order phase transition when coupled with controlled dissipation in the system. We study the properties of the phase transition using two- and three-dimensional setups to build a nanoscale quantum sensor that is especially robust against typical disorder imperfections or additional decoherence processes, with the sensitivity not being severely limited by the T2 decoherence time. Since our sensing protocol does not assume too many microscopic details of the process, one can easily apply this to other areas of quantum sensing and metrology. These results especially highlight the fact that dissipation in quantum systems, that is normally considered unwanted, can in fact be a powerful tool that allows us to enable a large list of quantum technologies in the future.

•Jan 1, 2020•1 citation

Cooling algorithms and mixed state phases of matter

Jerome Fergus Lloyd

This thesis develops new algorithms and theoretical frameworks for quantum many-body physics on near-term, noisy quantum simulators. The first half introduces dissipative "cooling algorithms" based on engineered dissipation to robustly prepare ground and thermal states. These protocols are demonstrated experimentally on Google's superconducting qubit processor, and analysed theoretically via effective quasiparticle theory and developments in connection to quantum detailed balance. The second half studies "mixed state phases" in classical non-equilibrium dynamics, and their connection to the conditional mutual information. A new numerical algorithm based on matrix-product states is introduced to compute this quantity for classical systems, and applied in the settings of spin systems quenched to high temperatures, and diffusive particle dynamics, providing new information-theoretic descriptions of non-equilibrium universality classes.

•Jan 1, 2026•0 citations

Ground-state preparation via nonlinear quantum dissipation

Alireza Ataei, Olle Eriksson, Vahid Azimi Mousolou

Ground-state preparation of quantum many-body systems is a fundamental challenge across quantum science, with implications for quantum simulation, quantum computing, and the study of complex quantum matter. The exponential growth of Hilbert space and the complexity of entangled eigenstates motivate the development of new approaches that go beyond conventional strategies based on adiabatic evolution, variational optimization, imaginary-time methods, and engineered dissipative processes. Here, we demonstrate that the recently proposed quantum Landau-Lifshitz-Gilbert (QLLG) dynamics [Phys. Rev. Lett. {\bf 133}, 266704 (2024)] provides an intrinsic nonlinear dissipative mechanism for real-time ground-state preparation. Unlike engineered dissipative schemes, QLLG encodes relaxation directly into the quantum equation of motion while preserving the underlying quantum structure of the evolution. The QLLG evolution selectively suppresses excited-state contributions, driving the system toward the lowest-energy eigenstate within the accessible symmetry sector. We show that the dynamics admits a monotonic energy functional and a stable ground-state fixed point, and that for generic initial states in an $N$-qubit Hilbert space the characteristic convergence time scales linearly with $N$ and inversely with the spectral gap. Numerical simulations of an interacting spin chain confirm our analytical predictions. These results establish nonlinear dissipative QLLG dynamics as a new avenue for quantum state preparation, opening a new route for quantum simulation, computation, and state engineering.

quant-pharXiv:2604.03731•Physical review. B./Physical review. B•Apr 7, 2026•0 citations

Dissipative quantum algorithms for excited-state quantum chemistry

Hao-En Li, Lin Lin

Electronic excited states are central to a vast array of physical and chemical phenomena, yet accurate and efficient methods for preparing them on quantum devices remain challenging and comparatively underexplored. We introduce a general dissipative algorithm for selectively preparing ab initio electronic excited states. The key idea is to recast excited-state preparation as an effective ground-state problem by suitably modifying the underlying Lindblad dynamics so that the target excited state becomes the unique steady state of a designed quantum channel. We develop three complementary strategies, tailored to different types of prior information about the excited state, such as symmetry and approximate energy. We demonstrate the effectiveness and versatility of these schemes through numerical simulations of atomic and molecular spectra, including valence excitations in prototypical planar conjugated molecules and transition-metal complexes. Taken together, these results provide a new pathway for advancing quantum simulation methods for realistic strongly correlated electronic systems.

quant-pharXiv:2512.19870•Journal of Chemical Theory and Computation•Dec 24, 2025•0 citations

Laser cooling of quantum systems

Javier Cerrillo Moreno

In this thesis novel methods for the laser cooling of quantum systems are presented. The use of quantum interference allows for the tailored cancelation of heating processes, so that an approximation to a cooling operator is possible that does not rely on the rotating wave approximation. This makes these schemes considerably faster and more efficient than existing ground state cooling methods, and allow for a significant relaxation of current experimental constraints. Several approaches are investigated in different systems. On the one hand, a special laser configuration, applicable to trapped ions, atoms or cantilevers, generates a double dark state that eliminates both the blue sideband and the carrier transition. As a consequence, vanishing phonon occupation up to first order in the perturbative expansion is achieved. Underlying this scheme is a combined action of two cooling schemes which makes the proposal very stable under parameter fluctuations. Its suitability as a cooling scheme for several ions in a trap or for a cloud of atoms in a dipole trap is shown. On the other hand, a pulsed cooling scheme for optomechanical systems is presented. It can be implemented for both strongly and weakly coupled optomechanical systems in both weakly and highly dissipative cavities. Its underlying mechanism is based on interferometric control of optomechanical interactions, and its efficiency is demonstrated with pulse sequences that are obtained by using methods from optimal control. Finally, it is shown how this pulsed method can be combined with continuous measurement to drive mechanical oscillators to highly squeezed steady states. Its mechanism relies on the modification of the dissipation and measurement terms, which drive the system towards a specific quadrature eigenstate. The scheme is robust to measurement inefficiencies and works also with highly dissipative cavities, which makes it accessible to implementation with state of the art technology.

•Jan 1, 2012•0 citations

Digital dissipative state preparation for frustration-free gapless quantum systems

Johannes Feldmeier, Yu-Jie Liu, Mikhail D. Lukin +1 more

Preparing algebraically correlated ground states of quantum many-body systems is an important, yet challenging task for quantum simulation. We introduce a protocol that employs local projective measurements and unitary feedback for frustration-free gapless systems. Our approach prepares a priori unknown ground states in time that scales polynomially with system size. We analytically show the performance our protocol for the dynamics of a single-particle; we argue the same mechanism generalizes to many-body systems based on the physics of quasiparticles. Our theory predicts that a transient cooling dynamics directly reveals the system's universal critical properties. In particular, the state preparation time is linear in the inverse of the finite-size gap (up to log correction) when the system's dynamical critical exponent is larger or equal the effective spatial dimension explored by the quasiparticles. We verify these predictions in numerical simulations of ferromagnetic Heisenberg models in one- and two dimensions, a Fredkin spin chain, and a two-dimensional model of resonating valence bond states. Our protocol stabilizes gapless many-body ground states fully digitally without requiring analog rotations, enabling access to high-fidelity states beyond conventional adiabatic approaches in near-term experiments.

quant-pharXiv:2603.10119•Mar 12, 2026•0 citations
The controlled preparation of quantum many-body states is a central challenge for quantum technologies. While preparing target states coherently is possible in principle, it is often fragile and experimentally demanding. Dissipative state preparation, where engineered environments drive the system toward desired steady states, provides a complementary and powerful paradigm. This thesis explores dissipative methods for preparing complex many-body states along three distinct directions. First, we investigate the dissipative stabilization of injective matrix product states (MPS). Injective MPS are particularly well suited for dissipative preparation because they arise as ground states of frustration-free parent Hamiltonians, allowing for tailored jump operators to steer the system directly into the target state. We showcase the surprising result that such state preparation works even in the dilute limit where steering only acts on a single link. Moreover, we introduce a formalism for engineering additional coherent interactions, extending the set of accessible states. Second, and complementary to steering, we develop and analyze a universal cooling scheme capable of preparing ground states even in frustrated quantum systems. In contrast to steering methods, universal cooling can overcome the glass floor that forbids steering methods to prepare such frustrated ground states. A key insight here is that the presented cooling scheme is completely system-agnostic making it extremely robust. Finally, we pursue dressing of the system eigenstates by means of either classical drives or coherent interactions as a means to influence the action of dissipation on the system. Focusing first on time-dependent systems, we propose a generalized numerical implementation of non-adiabatic master equations suitable for the use of optimal control tools. Additionally, we investigate how the collective coupling between a spin ensemble and a cavity can steer the system into a spin-squeezed steady state. Together, these three avenues illustrate how tailored dissipative dynamics can extend the frontier of many-body state preparation, from stabilizing injective MPS to cooling complex frustrated systems and generating non-classical steady states in the dressed framework.
Quantum systems cannot always be treated as isolated from their surroundings since this is an idealization which is not always true. Though theoretical analysis of open quantum systems poses great challenges as one needs to treat many-particle quantum systems as a whole, the system-environment interactions often lead to many interesting effects that are not observed in closed systems. The dissipation of a quantum system is not always a disadvantage and, in fact, if exploited properly in combination of coherent driving, one can steer the system into a desired state. This dissipation driven quantum state engineering technique finds its applications in novel technologies such as quantum computing, quantum simulation, and quantum metrology. In this thesis, we focus on the latter two, and show that using dissipative channels allows us to build quantum devices that have considerable advantages over their entirely coherent analogues. Simulation of many-body problems on a quantum simulator will unlock the potential to provide great insights into a large number of systems especially those that are computationally intractable or experimentally challenging. The two crucial steps towards the successful functioning of quantum simulation are the initialization of the quantum simulators i.e, preparing the system in a known initial state, and the Hamiltonian engineering. While there have been many experiments demonstrating the implementation of the Hamiltonian dynamics on the quantum simulator, work still needs to be done on the problem of preparing the simulator in a suitable quantum state. This is exactly our aim here and we propose a protocol to cool a given system into the ground state of a black-box spin Hamiltonian. The central idea is to use a dissipatively driven auxiliary spin to pull out the excitations in the system, eventually cooling it to its ground state. We show that already a single auxiliary spin is efficient in cooling the quantum simulator to a low-energy state of largely arbitrary Hamiltonians as the resources scale only polynomially with the system size. We also show that our scheme of sympathetic cooling is robust against additional sources of decoherence. The second part of the thesis deals with nanoscale quantum sensing using dissipative first order transition in the magnetization of a system of nitrogen-vacancy point defect centers in diamond. The sensitivity of a generic quantum sensor with non-interacting particles scales as the square root of the number of particles. Therefore, a sensor with large number of particles displays a better sensitivity. However, in the interest of nanoscale sensing, having a large number of particles implies that they are closely packed next to each other. At such high densities, the particles interact strongly with each other posing great challenges to the sensing process. Here, we show that these interactions can in fact be used to trigger a first order phase transition when coupled with controlled dissipation in the system. We study the properties of the phase transition using two- and three-dimensional setups to build a nanoscale quantum sensor that is especially robust against typical disorder imperfections or additional decoherence processes, with the sensitivity not being severely limited by the T2 decoherence time. Since our sensing protocol does not assume too many microscopic details of the process, one can easily apply this to other areas of quantum sensing and metrology. These results especially highlight the fact that dissipation in quantum systems, that is normally considered unwanted, can in fact be a powerful tool that allows us to enable a large list of quantum technologies in the future.
This thesis develops new algorithms and theoretical frameworks for quantum many-body physics on near-term, noisy quantum simulators. The first half introduces dissipative "cooling algorithms" based on engineered dissipation to robustly prepare ground and thermal states. These protocols are demonstrated experimentally on Google's superconducting qubit processor, and analysed theoretically via effective quasiparticle theory and developments in connection to quantum detailed balance. The second half studies "mixed state phases" in classical non-equilibrium dynamics, and their connection to the conditional mutual information. A new numerical algorithm based on matrix-product states is introduced to compute this quantity for classical systems, and applied in the settings of spin systems quenched to high temperatures, and diffusive particle dynamics, providing new information-theoretic descriptions of non-equilibrium universality classes.
Ground-state preparation of quantum many-body systems is a fundamental challenge across quantum science, with implications for quantum simulation, quantum computing, and the study of complex quantum matter. The exponential growth of Hilbert space and the complexity of entangled eigenstates motivate the development of new approaches that go beyond conventional strategies based on adiabatic evolution, variational optimization, imaginary-time methods, and engineered dissipative processes. Here, we demonstrate that the recently proposed quantum Landau-Lifshitz-Gilbert (QLLG) dynamics [Phys. Rev. Lett. {\bf 133}, 266704 (2024)] provides an intrinsic nonlinear dissipative mechanism for real-time ground-state preparation. Unlike engineered dissipative schemes, QLLG encodes relaxation directly into the quantum equation of motion while preserving the underlying quantum structure of the evolution. The QLLG evolution selectively suppresses excited-state contributions, driving the system toward the lowest-energy eigenstate within the accessible symmetry sector. We show that the dynamics admits a monotonic energy functional and a stable ground-state fixed point, and that for generic initial states in an NNN-qubit Hilbert space the characteristic convergence time scales linearly with NNN and inversely with the spectral gap. Numerical simulations of an interacting spin chain confirm our analytical predictions. These results establish nonlinear dissipative QLLG dynamics as a new avenue for quantum state preparation, opening a new route for quantum simulation, computation, and state engineering.
Electronic excited states are central to a vast array of physical and chemical phenomena, yet accurate and efficient methods for preparing them on quantum devices remain challenging and comparatively underexplored. We introduce a general dissipative algorithm for selectively preparing ab initio electronic excited states. The key idea is to recast excited-state preparation as an effective ground-state problem by suitably modifying the underlying Lindblad dynamics so that the target excited state becomes the unique steady state of a designed quantum channel. We develop three complementary strategies, tailored to different types of prior information about the excited state, such as symmetry and approximate energy. We demonstrate the effectiveness and versatility of these schemes through numerical simulations of atomic and molecular spectra, including valence excitations in prototypical planar conjugated molecules and transition-metal complexes. Taken together, these results provide a new pathway for advancing quantum simulation methods for realistic strongly correlated electronic systems.
In this thesis novel methods for the laser cooling of quantum systems are presented. The use of quantum interference allows for the tailored cancelation of heating processes, so that an approximation to a cooling operator is possible that does not rely on the rotating wave approximation. This makes these schemes considerably faster and more efficient than existing ground state cooling methods, and allow for a significant relaxation of current experimental constraints. Several approaches are investigated in different systems. On the one hand, a special laser configuration, applicable to trapped ions, atoms or cantilevers, generates a double dark state that eliminates both the blue sideband and the carrier transition. As a consequence, vanishing phonon occupation up to first order in the perturbative expansion is achieved. Underlying this scheme is a combined action of two cooling schemes which makes the proposal very stable under parameter fluctuations. Its suitability as a cooling scheme for several ions in a trap or for a cloud of atoms in a dipole trap is shown. On the other hand, a pulsed cooling scheme for optomechanical systems is presented. It can be implemented for both strongly and weakly coupled optomechanical systems in both weakly and highly dissipative cavities. Its underlying mechanism is based on interferometric control of optomechanical interactions, and its efficiency is demonstrated with pulse sequences that are obtained by using methods from optimal control. Finally, it is shown how this pulsed method can be combined with continuous measurement to drive mechanical oscillators to highly squeezed steady states. Its mechanism relies on the modification of the dissipation and measurement terms, which drive the system towards a specific quadrature eigenstate. The scheme is robust to measurement inefficiencies and works also with highly dissipative cavities, which makes it accessible to implementation with state of the art technology.
Preparing algebraically correlated ground states of quantum many-body systems is an important, yet challenging task for quantum simulation. We introduce a protocol that employs local projective measurements and unitary feedback for frustration-free gapless systems. Our approach prepares a priori unknown ground states in time that scales polynomially with system size. We analytically show the performance our protocol for the dynamics of a single-particle; we argue the same mechanism generalizes to many-body systems based on the physics of quasiparticles. Our theory predicts that a transient cooling dynamics directly reveals the system's universal critical properties. In particular, the state preparation time is linear in the inverse of the finite-size gap (up to log correction) when the system's dynamical critical exponent is larger or equal the effective spatial dimension explored by the quasiparticles. We verify these predictions in numerical simulations of ferromagnetic Heisenberg models in one- and two dimensions, a Fredkin spin chain, and a two-dimensional model of resonating valence bond states. Our protocol stabilizes gapless many-body ground states fully digitally without requiring analog rotations, enabling access to high-fidelity states beyond conventional adiabatic approaches in near-term experiments.