In PASQuanS2.1, we focus on the three quantum simulation platforms using individual atoms as their central quantum resource. These are:
- mobile neutral atoms in optical lattices interacting by collisions;
- position-controlled neutral atoms in optical tweezers interacting over long distances via Rydberg states;
- and trapped ions interacting electrostatically and by optical coupling to common motional degrees of freedom.
The three platforms share the technological base, i.e., laser technology, control electronics, vacuum technology and cryogenics, but offer different problem-specific specialisations, opportunities and advantages.
Current limitations differ for the three platforms, which makes the scientific objectives regarding the advancement of the underlying technologies partly platform specific. However, our high-level objectives target three overarching aims in a synergistic form:
- development of the platforms;
- expansion of end-use cases and their bespoke software stacks;
- and expansion of the end-user community and public awareness of quantum simulation.
More specifically, we are aiming to achieve the following technological advancements in the entire PASQuanS2 FPA, and more specifically in this first phase of PASQuanS2.1:
Scaling up the system size without loss of control and readout fidelity
Fermionic systems aim to reach particle numbers up to 10,000 atoms at the end of the FPA, with already more than 2000 atoms in this SGA1. At these system sizes, validation of the prepared quantum states becomes highly non-trivial and efficient methods need to be developed and demonstrated. This may include quantum verification, for example, via the preparation of two identical systems which are brought to interference before detection or randomised benchmarking techniques.
Rydberg atom-based simulators offer full control of the array geometry, albeit for smaller atom numbers. Here the scaling goal is to reach 1000 atoms in a production-quality simulator that can run in a fully automated form at the end of the FPA, with already 1000 atoms demonstrated in a laboratory system at the end of this PASQuanS2.1.
Ions offer the highest control fidelities and a platform for testing quantum simulation technologies but provide the smallest atom numbers. By the end of the FPA in seven years, we aim to realize linear strings with up to 100 ions for these platforms and to develop a 2D geometry with up to 300 ions, with already 100 ions entangled in 1D and 200 atoms trapped in a 2D architecture at the end of PASQuanS2.1. This will facilitate technology transfer (e.g., of optical addressing systems, control electronics and modularized photonic systems) to our production-level neutral atom platforms.
Improving the simulation fidelity and data rate
This objective has multiple aspects which are platform specific, with an emphasis on improving the level of quantitative control, the calibration, and the coherence. The Rydberg and ion platforms will improve their coherence and storage times by utilising cryogenic environments and improved vacuum systems. At the end of the FPA, the state preparation and readout infidelity will reach the 10-3 level for the optical lattice and Rydberg platforms, of which we already plan to reach this level in first demonstrations in PASQuanS2.1. On the same platforms the data rate will be increased by an order of magnitude at the end of the FPA, with an increase of more than a factor of two already achieved in PASQuanS2.1.
Standardisation of control interfaces and data storage formats
Implementing external access to quantum simulators via a standardised programming interface is particularly challenging. This is rooted in their analogue nature, where the system Hamiltonian of interest is implemented directly and is strongly hardware dependent. This makes it harder and less obvious to introduce a unifying abstraction layer for the control interface. Nevertheless, for external user access (cloud or local), such a layer is required. The development of a standardised interface will further facilitate the integration of optimal control algorithms, which promise unique solutions to push preparation and readout fidelities.
Similarly, the formats used for data storage of quantum simulation results are highly platform-specific. This complicates efficient data exchange. Up to date, data is exchanged among researchers via direct personal contact and detailed communication of the details of the quantum simulation and hardware. We aim to develop unifying concepts for both control interfaces and data storage formats.
Widening the scope of analogue quantum simulators
The scope of today's quantum simulators is strongly limited, typically to a few global control parameters of the implemented physical Hamiltonian. We will improve the local control capabilities on all involved platforms. For the optical lattice system, we aim to demonstrate local tunnelling control and improve the control of local potentials; for the Rydberg platform, high fidelity dynamic control of local fields and spatial control of the interactions; for the ion platform control of the interaction range.
Furthermore, analogue simulation of low-temperature phases, mostly relevant to fermionic simulators, is limited by the minimum temperature or entropy that can be reached. To simulate long-range correlated fermionic systems, we aim to develop new methods during PASQuanS2.1 that will allow us to reduce the system temperature by at least an order of magnitude at the end of the FPA. At the same time, we plan to investigate how to harness the unique advantage of being able to directly employ “fermionic qubits” that do not carry any overhead for implementing many real-world problems, e.g., material science and in quantum chemistry.
Cloud access to quantum simulator demonstrators
We aim to demonstrate cloud access to at least two of the three types of quantum simulators of PASQuanS2 at the end of the FPA. To reduce the required person-power and enhance the uptime of the machines, this requires improvement in the automatization, system integration and monitoring infrastructures for all architectures with many synergies in the required hardware. All these tasks will already be addressed during PASQuanS2.1.
The goal is to achieve autonomous operation of the simulators for at least 24 hours without human intervention, which we already plan to demonstrate in specific simulators during this first SGA1. Another important aspect is the maintainability of the simulators. During PASQuanS2.1, we will address this issue through the development of modularised components providing ready-to-use solutions for the optical, electrical, and mechanical sub-systems of the machines.
Verifying quantitative quantum simulation in regimes of quantum advantage
We will implement and further develop novel measurement protocols and bring methods for characterisation, verification, and certification of Hamiltonians to the experimental platforms. In particular, we will build on methods initially introduced by the predecessor project PASQuanS and in recent literature, including randomised and optimised measurements and methods of robust Hamiltonian learning techniques in regimes that are not classically efficiently tractable.
These techniques need to be developed theoretically from first Hamiltonian and then Liouvillian learning and then brought to experimental platforms. From our work in PASQuanS, we understand the platforms to be operating in regimes of quantum advantage, at least for many-body dynamics problems. This will provide a controlled, verified operation of our platforms in regimes of quantum advantage.
Development of a full software stack
In the complete PASQuanS2 FPA, we will address the full stack of software necessary to run programmable, optimised, error-mitigated, verifiable and measurable quantum simulators. At the highest level, this software stack will allow for the implementation and solution of specific problems without the user needing to understand the detailed workings.
At lower levels, this involves the implementation of software to run specific problems on hardware, with the inclusion of optimal control methods for controlling the hardware. During PASQuanS2.1, we will set the basis for this full software stack, implementing first versions already for specific quantum simulations.
Development of digital twins
Validation, verification, and benchmarking of quantum simulators will benefit strongly from the development of machine-specific digital models, which map the system-specific noise sources as accurately as possible. This will allow for a direct comparison of the simulation results for small-scale simulations that are numerically tractable.
The modelling will also aid in the development of control strategies to minimize the impact of the system noise and maximise the coherence of the quantum simulator. We will demonstrate a digital twin for at least one of the platforms during PASQuanS2.1 already.