Periodic Reporting for period 1 - EBQM (Ergodicity Breaking in Quantum Matter: From Many-Body Localisation to Quantum Glasses)
Período documentado: 2021-09-01 hasta 2023-08-31
Left to their own devices, typical physical systems will eventually reach thermal equilibrium with their
environment. While a familiar feature of life in the classical world – think of ice melting in a drink, or coffee
cooling to room temperature – this process of thermalisation can pose a serious problem for quantum technologies.
When a physical system thermalises, any information once contained in it is scrambled, essentially lost to the
environment - the coffee does not ‘remember’ it was once hot, nor does the drink ‘remember’ it once contained an
ice cube. The same principle holds true for quantum systems: if they undergo thermalisation, they will effectively
have lost all information about how they were initially prepared. For future quantum technologies which will rely
on the storage and retrieval of information (such as quantum computers), this loss of memory could be disastrous.
One way to prevent a quantum system from thermalising is the addition of disorder. Disorder in quantum systems
can come in many forms, from chemical impurities in solid-state materials through to the random speckle patterns
of light used in ultracold atomic gas experiments, and has been the focus of a great deal of recent study as it holds
great promise for the development of robust new quantum technologies.
The main aim of this project was to explore novel ways that disorder could lead to novel mechanisms to inhibit
thermalisation in near-future quantum technologies and be used to engineer stable quantum memories. Doing so required the development of an advanced new computational technique
which led to the ability to simulate extremely large quantum systems up to extremely long timescales. The final results of the project
support the existence of a long-lived quantum memory in one dimension in the presence of both random and pseudo-random 'disorder'.
By contrast, in two dimensions it appears that the pseudo-random 'disorder' leads to significantly more stable quantum memory effects
than purely random disorder. This has important implications for the future development of robust quantum memories for use in future quantum technologies.
environment. While a familiar feature of life in the classical world – think of ice melting in a drink, or coffee
cooling to room temperature – this process of thermalisation can pose a serious problem for quantum technologies.
When a physical system thermalises, any information once contained in it is scrambled, essentially lost to the
environment - the coffee does not ‘remember’ it was once hot, nor does the drink ‘remember’ it once contained an
ice cube. The same principle holds true for quantum systems: if they undergo thermalisation, they will effectively
have lost all information about how they were initially prepared. For future quantum technologies which will rely
on the storage and retrieval of information (such as quantum computers), this loss of memory could be disastrous.
One way to prevent a quantum system from thermalising is the addition of disorder. Disorder in quantum systems
can come in many forms, from chemical impurities in solid-state materials through to the random speckle patterns
of light used in ultracold atomic gas experiments, and has been the focus of a great deal of recent study as it holds
great promise for the development of robust new quantum technologies.
The main aim of this project was to explore novel ways that disorder could lead to novel mechanisms to inhibit
thermalisation in near-future quantum technologies and be used to engineer stable quantum memories. Doing so required the development of an advanced new computational technique
which led to the ability to simulate extremely large quantum systems up to extremely long timescales. The final results of the project
support the existence of a long-lived quantum memory in one dimension in the presence of both random and pseudo-random 'disorder'.
By contrast, in two dimensions it appears that the pseudo-random 'disorder' leads to significantly more stable quantum memory effects
than purely random disorder. This has important implications for the future development of robust quantum memories for use in future quantum technologies.
The main scientific and technological achievement is the development of the Tensor Flow Equation (TFE) technique, a novel numerical method for the simulation of complex quantum systems on classical computers. In particular, this numerical method leverages the massively parallel power of graphics processing units (GPUs) to approximately diagonalise (‘solve’) many-body quantum systems in a computationally efficient way, allowing us to compute the non-equilibrium dynamics of large complex systems up to extremely long timescales. This enabled a detailed investigation of quantum memory effects in both one- and two-dimensional quantum systems.
The improvements came in the form of two main breakthroughs, one technological and one conceptual. On a technological level, the method was entirely rewritten to leverage the massively parallel processing capabilities of modern graphics processing units (GPUs) to deliver performance that cut the simulation time by several orders of magnitude over the CPU-based version of the technique. On a conceptual level, the regime of validity of the technique has been hugely enhanced by the development of scrambling transforms, which take a method designed for strongly disordered quantum systems and turn it into a technique which can simulate even entirely homogeneous, non-disordered matter. Secondarily, this development also enhances the speed and efficiency of the technique, delivering vital performance improvements that allow cutting edge high performance computing hardware to be pushed close to its limits.
The main results of the work include the following: the development of the TFE technique and its extension to run on GPUs; the introduction of 'dilute disorder' as a phenomenological bridge between random and homogeneous systems, allowing the systematic investigation of rare-region effects; the detailed numerical investigation of how continuous non-Abelian symmetries can affect localisation and potentially lead to its demise over extremely long timescales; the development of a technique to experimentally reconstruct the building blocks of many-body localisation, an enigmatic phase of matter with many counter-intuitive properties; an investigation into the phenomenology of localisation in disorder-free systems and the finding that these materials exhibit qualitatively different behaviour that may imply slow loss of memory over very long timescales, and finally the finding that quantum memory effects appear to persist in two dimensions to long (but not necessarily infinitely long) times provided the disorder is pseudo-random rather than truly random. These results constitute some early steps towards the challenging process of connecting glassiness with many-body localisation.
The improvements came in the form of two main breakthroughs, one technological and one conceptual. On a technological level, the method was entirely rewritten to leverage the massively parallel processing capabilities of modern graphics processing units (GPUs) to deliver performance that cut the simulation time by several orders of magnitude over the CPU-based version of the technique. On a conceptual level, the regime of validity of the technique has been hugely enhanced by the development of scrambling transforms, which take a method designed for strongly disordered quantum systems and turn it into a technique which can simulate even entirely homogeneous, non-disordered matter. Secondarily, this development also enhances the speed and efficiency of the technique, delivering vital performance improvements that allow cutting edge high performance computing hardware to be pushed close to its limits.
The main results of the work include the following: the development of the TFE technique and its extension to run on GPUs; the introduction of 'dilute disorder' as a phenomenological bridge between random and homogeneous systems, allowing the systematic investigation of rare-region effects; the detailed numerical investigation of how continuous non-Abelian symmetries can affect localisation and potentially lead to its demise over extremely long timescales; the development of a technique to experimentally reconstruct the building blocks of many-body localisation, an enigmatic phase of matter with many counter-intuitive properties; an investigation into the phenomenology of localisation in disorder-free systems and the finding that these materials exhibit qualitatively different behaviour that may imply slow loss of memory over very long timescales, and finally the finding that quantum memory effects appear to persist in two dimensions to long (but not necessarily infinitely long) times provided the disorder is pseudo-random rather than truly random. These results constitute some early steps towards the challenging process of connecting glassiness with many-body localisation.
This work significantly advances the state-of-the-art of classical simulations of quantum matter, enabling the simulation of large systems to unprecedentedly long times. This combination allows us to reach parameter regimes inaccessible to other contemporary methods, and allows us to perform careful finite-size scaling analyses of the stability of various phases of matter. The impact of this work reaches far beyond the community of disordered systems researchers, and impacts all fields of many-body physics that rely on the dynamical simulation of complex quantum systems, even including fields such as quantum chemistry. This work also poses a strong challenge to claims of quantum advantage, as it demonstrates a powerful new avenue for the classical simulation of quantum matter. By leveraging novel accelerators such as GPUs, this work has clearly demonstrated that there is significant scope for continued development of classical techniques for the foreseeable future.
This result pave the way for future developments in engineering stable quantum memories in real-world systems that can be used in practical quantum technologies of the future.
This result pave the way for future developments in engineering stable quantum memories in real-world systems that can be used in practical quantum technologies of the future.