CERN has recently launched its Quantum Technology Initiative (QTI) to coordinate its contribution in the rapidly advancing landscape of quantum technologies and coordinate activities with other global players in the field. We discussed with Michael Doser, co-coordinator of the quantum sensing strand of the QTI and the EP Department’s representative, about the key challenges and planned activities.

CERN's QTI is in line with the EPPSU recommendations for a diverse R&D and physics programme building on new technologies that will complement the efforts towards the next generation of colliders. Moreover, ECFA has launched a dedicated R&D Detector Programme that includes a panel on quantum sensors that Doser jointly convenes with Fermilab's Anna Grasselino and with Marcel Demarteau (ORNL). In addition, CERN’s EP Department has launched a 5-year programme on Detector Technologies R&D to advance detector technologies relevant for the next generation of high-energy physics experiments. Doser explains that the main goal is to promote the alignment of these efforts right from the start and maximize their impact for the future of the high-energy physics community.

CERN’s Quantum Technology Initiative covers four large distinct domains, namely quantum computing, quantum information, quantum theory and quantum sensors. Doser helps us understand the meaning of each of these terms. He explains: “Quantum computing has seen a very high pace of development over the past decades with many efforts currently ongoing involving academia and the industrial sector to demonstrate quantum supremacy. There are already many particle physics groups looking into how to exploit the potential of these technologies and implement them for high energy physics.” and continues “Quantum information is related to the communication and safe transmission of data and traditionally is tied to cryptography. This strand addresses the potential of quantum-based technologies to transform computing, security and communications”. Quantum theory offers the theoretical basis for this communication, including the development of algorithms to exploit the potential of quantum technologies; in the framework of QTI the goal is also to think of applications that can be useful for high-energy physics, but also to explore novel approaches to testing the standard model as well as its foundations using techniques that are now becoming possible. Finally, quantum sensing describes how we can use a quantum system and certain quantum phenomena to measure a physical quantity. Historical examples of quantum sensors include magnetometers based on superconducting quantum interference devices and atomic vapors, or atomic clocks with the most common platforms being spin qubits, trapped ions and flux qubits. Doser adds that “quantum sensing has been on the radar of many states for quite a long time and recently quantum sensing has become a distinct and rapidly growing branch of research within the area of quantum science and technology. The US but also the UK have already launched the process of looking into what quantum sensors can bring to particle physics”.

Importantly, Doser notes that “those four topics are not individual towers but intertwined fields of research”. His mandate is to look into ongoing projects working in the field of quantum sensing technology and their relevance for particle physics research both at the low- and high-energy spectrum. A key challenge will be to smoothly integrate these activities into CERN’s core accelerator-based activities and furthermore exploit opportunities for the involvement of EP Department’s Detector Technology group. Synergies with ongoing low-energy experiments at CERN also exist, as Doser notes: “A number of activities already taking place at CERN’s AD or ISOLDE facility were further discussed and encouraged in the framework of the Physics Beyond Colliders programme that was launched five years ago’.

There is an overlap in the goals of particle physics at the low-energy and high-energy end of the spectrum with regards to investigations into some of the most pressing open questions, such as the nature of dark matter and the form that new physics could have. For Doser, “the goal is to bring together people from CERN and other laboratories through the Quantum Initiative and go through the potential of certain quantum technologies developed both for the low-energy physics programme at CERN as well as for future physics experiments at the energy frontier”. Many of the proposed technologies are often at the edge of what is feasible, but may well end up becoming more widespread in the more distant future. Therefore it is important to understand which aspects of a detector can be beneficial for future physics analyses. “Does it make sense to aim for sub-mιcron tracking resolution or for individual (low energy) photon detection? Should we invest in completely blue-sky detector technologies that might for example be sensitive to the spin of a particle produced in collisions or apply non destructive techniques for measuring a particle’s properties?” asks Doser? Clearly formulating these questions and trying to find the right answers is one of the key goals of the QTI initiative.

In parallel, for Doser it is important to interact with the detector groups and understand where their interest lies and how the directions foreseen in the R&D programme pursued by CERN’s EP can profit from looking into quantum technologies. “One example is the development of scintillating detectors and the ongoing efforts to improve the scintillation yield by studying the feasibility of using nanodots or of nanodiamonds, nanostructures able to produce more light per unit thickness than standard scintillators and that furthermore offer much better time resolution. At a number of collider or accelerator-based experiments, particularly this point – trying to reach time resolutions of the order of 10 ps – is turning out to be central for future approaches to particle identification, as are ways of dealing with very high charged particle multiplicities, pile-up and multiple vertices, together with the high secondary charge densities that ensue in detectors”. Looking at the big picture, the detector requirements differ between low and high-energy physics experiments in many ways: while at low energies, maximal sensitivity to single minute changes of individual atoms is well matched to the exquisite sensitivity offered by quantum sensors, at high energies, the large number of charges produced by the interaction of a high energy particle with bulk matter would rather favor attempting to enhance signal yield while reducing detector thicknesses. But also data acquisition might be affected: a number of atomic and quantum optic groups are working on the development of non-triggered alternative data control and acquisition systems that may end up becoming a model for future low-energy experiments at CERN. “These are small steps that can be brought in for the benefit of particle physics both at low and high-energy frontiers” concludes Doser.

The R&D programme on Detector Technologies launched by ECFA will encourage R&D on detectors for high-energy physics experiments that could also be beneficial for the low-energy regime. However, Doser highlights that specific technologies can be beneficial for both ends of the energy spectrum. “Imagine that you are searching for axions through the search of photons produced as the axions interact with an electromagnetic field of a specific frequency in a cavity. In that case you would like your detector to be tuned to photons of a specific frequency as otherwise you will not observe them. In the absence of knowing exactly where to look, you would however need a tunable microwave cavity that would allow you to search over a broader range of frequencies. This technology is unlikely to be useful for high-energy physics experiments but might end up, through the material science involved with producing such systems, end up having an impact of accelerating cavities. Another example could be cryogenic electronics, which are used with great effect to search in a novel manner for axions; being able to develop such systems in a way that would allow them to be used the way CMOS technologies are could enable building charged particle or photon detectors based on cryogenic technologies, such as superconducting nanowire single particle detectors (SNSPD), but might simply end up allowing extending existing approaches to temperatures at which radiation damage would no longer be a concern.” Doser argues that it is imperative to explore technologies that may even lie beyond what is currently thought to be feasible as they could profit searches both at the low and high-energy regime. “At the end experiments at both the low and high-energies have the same goal of addressing those questions that the discovery of the Higgs boson has now pushed to the center of the stage: the nature of dark matter, the foundations upon which the standard model is built, the consistency of our understanding at all energy scales”.

We ask Doser whether quantum sensors can be used in the next generation of high-energy physics experiments. “This brings me back to what we discussed in the beginning: quantum sensing is actually based on the feasibility of observing a single atom or particle after an external perturbation has changed its state. Possible outcomes include a change in the state or the orientation of the spin or the emission of photons at a certain wavelength. A device that could detect such weak changes without destroying the system can be called a quantum sensor.  Οne could argue that high-energy physics is not about the detection of the smallest possible change of a quantum system". On the contrary: “The ionization signals underlying high energy detectors stem from the particle you are trying to detect having stripped off electrons from a large number of atoms and what you actually detect is the pulse of current corresponding to the flow of these electrons towards your amplifier. Therefore the question that needs to be asked is whether developing detectors that will be sensitive to one electron can be beneficial to high-energy physics. I think that the answer can be yes in a number of cases, as mentioned earlier, but we must also understand the limititations in how much we can improve with quantum sensing compared to existing technologies. However, it is equally important to understand that the experiments at the low-energy end of the spectrum explore in many ways the same landscape as high-energy experiments, albeit using different approaches. They are in many cases looking for the same things, often indirectly (through searches for rare decays or for symmetry breaking observables, such as electric dipole moments), but sometimes directly (in the case of searches for very light dark matter candidates), and are clearly complementary.”

Finally, Doser emphasises the importance of collaboration both with other communities with long-standing expertise in atomic physics or quantum optics, as well as with industry. Beyond the obvious interest in exploring the potential of future quantum computers, a development driven very strongly by industry, or the use of ultra-sensitive quantum sensors in, e.g. of ensuring ultra-precise magnetic field stability, there are other, less obvious areas of interest where also CERN’s expertise or focus might benefit other communities. As an example he refers to the potential interest of having highly accurate timing that can be used by a number of experiments at CERN. “The communities of atomic physics and quantum optics are expanding a timing network across Europe and I think that it is worthwhile looking into how CERN could be part of such a network, with benefits for the ISOLDE and AD experiments but also potentially for collider-based activities. An external clock providing a reference time with sub-picosecond precision could enable ultra-high precision time-stamping of detector signals for continuous readout, or might enable (in concert with appropriate detectors) time-of-flight particle-identification up to very high energies. Incorporating such a technology at the event rates and for the numbers of sensors that the next generations of detectors will require however dramatically scaling up what is currently possible, an effort that could in turn benefit the original communities and will necessarily involve industrial partners.”

To develop the expertise necessary to think of implementing quantum technologies at CERN, a number of initiatives are being initiated aiming to offer a deeper understanding of the role that quantum technologies could play for CERN and of inspiring ideas and new collaborations. The first was a successful series of introductory lectures into quantum computing that ran in November and December last year [https://home.cern/news/announcement/computing/online-introductory-lectures-quantum-computing-6-november]. Doser together with Maurizio Pierini are working to follow upon them with a new series of lectures on quantum sensing technologies later this year.

In 1959, the quantum physicist and later Nobel laureate Richard Feynman gave a much-cited lecture “There’s Plenty of Room at the Bottom” which outlined how future technologies could operate on a micro- and nanoscopic scale. It seems that today we are at the dawn of a new era for exploring their potential, with many opportunities to shape this process.

For more information: https://quantum.cern/