Fermilab, along with several partnerships and collaborations, is investigating the use of quantum computing to ramp up computing power in a number of initiatives. Quantum computing, if harnessed, could revolutionize particle physics, solving problems in a matter of minutes that may take centuries to solve using traditional computers. It could also open doors into new realms of physics, solving mysteries that have tantalized scientists for decades.
Axion dark matter detection using quantum computing technology
Dark matter makes up more than a quarter of the universe, and scientists have come up with a number of models that predict what, exactly, dark matter is. One candidate is a postulated particle called an axion.
The very lightweight axion particle is predicted a theory that could explain the long-standing puzzle of why the neutron has no electric dipole moment, a term for a separation of electrical charges. The presence of an axion could explain the absence of an EDM.
In rare events, dark matter composed of axions can scatter on strong magnetic fields to create single microwave particles of light, called photons, of frequency equal to the axion mass.
Fermilab’s ADMX experiment is already conducting an initial search for these exotic particles using the world’s lowest-noise radio receiver, operated at a temperature near absolute zero. However, as the experiment proceeds to search at higher frequencies, the radio noise due to the jitter of the quantum vacuum will mask the tiny expected signals.
Superconducting qubits, which have been developed for quantum computing, may be the key to detecting the elusive axion dark matter. These “artificial atoms” are engineered to manipulate single microwave photons, which encode the data of the computation. The quantum computer can be configured to receive single photons not from other qubits within the quantum computer, but rather from the dark matter source. The high fidelity required for robust quantum computing then translates into efficient detection of the axion signal. Moreover, qubits can detect microwave photons by indirectly sensing them and avoiding the quantum jitter; they can thus achieve the low noise levels required for future axion experiments.
Superconducting quantum systems
Quantum systems that use the phenomenon of superconductivity are at the forefront of quantum computing, quantum sensing and various planned fundamental physics experiments.
These systems rely on the superposition of quantum states, which eventually collapse into a single state. The effectiveness of quantum systems depends a great deal on the length of time the superposition state survives, a quantity called coherence time. The longer the coherence time, the more time is available for the quantum system to perform operations.
For quantum computing, 3-D circuit architecture of qubits — units of quantum information — currently holds the highest coherence times among all superconductivity-based qubits.
A key enabling part of this architecture is 3-D-microwave resonators, structures that store and allow manipulation of electromagnetic fields. The resonators’ ability to retain energy can be measured by something called the quality factor, or Q, which directly affects the achievable coherence times. Fermilab is the world leader in both the underlying science and building and operating the full-scale particle accelerators based on ultrahigh-Q superconducting radio-frequency (SRF) resonators. We are working to apply this expertise to the field of quantum systems.
The current state-of-the-art Q value for quantum computing systems is roughly 1x108, corresponding to coherence times of about 1 millisecond. Fermilab-designed and surface engineered SRF resonators, built for accelerators, routinely achieve a Q value of more than 3x1010 in the broad range of microwave fields, with record cavities possessing a Q of more than 2x1011. This is more than 1,000 times better than best resonators currently employed in quantum computing. If such Q factors could be directly translated to the quantum regime, the potential coherence times of such SRF/3-D qubits could be more than 1 second, enabling a range of qualitatively different capabilities of quantum computing.
One of the main goals of Fermilab’s Superconducting Quantum Systems program is to demonstrate such ultrahigh-Q SRF/3-D qubits with the record long coherence times, and ultimately to put a number of them together in a multiqubit “quantum computer” type system. For this effort, we have current collaborations with the University of Wisconsin-Madison, and the National Institute of Standards and Technology.
Fermilab Quantum Teleportation Experiment
FQNet is a quantum teleportation experiment, and its initial phase is based on commercial optical fibers used to distribute a property called entanglement across distances of tens of kilometers.
In quantum entanglement, two or more particles are inextricably linked to each other, so that a description of one necessarily implies a description of the others. That is, one particle cannot be described independently of the others. This entanglement can occur even when the particles are separated by large distances, and to describe it, Albert Einstein coined the phrase "spooky action at a distance."
Entanglement is also a property of certain systems of qubits, which are units of quantum information.
FQNET will explore the entanglement phenomenon over a long distance. It will be used for R&D on future quantum communication technologies and protocols. Advancements in quantum networking have the potential to revolutionize computation, communication and even our fundamental understanding of space-time.
The FQNET experiment was launched as part of the INQNET research program. INQNET fosters fundamental quantum information science and technologies under the Alliance for Quantum Technologies, co-founded by Caltech and AT&T’s Palo Alto Foundry innovation centers.
Studying the cosmos with MAGIS-100
Fermilab seeks to host MAGIS-100 — the 100-meter Matter-wave Atomic Gradiometer Interferometric Sensor — which will test quantum mechanics on macroscopic scales of space and time.
The laboratory is developing a sensitive prototype detector that could help scientists precisely measure properties of the cosmos.
One of these is dark matter. Physicists have offered a number of mathematical models describing dark matter, a mysterious substance that makes up more than a quarter of the universe. Some of these models suggest that dark matter might be made of ultralightweight particles. MAGIS-100 will be used to study these models, in particular those that predict varying atomic energy levels.
A longer-term goal for MAGIS-100 is to establish the sensitivity of its measurement technique to gravitational waves in the frequency range around 1 hertz, where there are few existing or proposed detectors. Gravitational waves, predicted by Einstein a century ago but discovered for the first time only in 2015, are ripples in space-time caused by accelerating masses, such as stars and galaxies. MAGIS-100 creates atom matter waves in superposition separated by up to 10 meters.
The MAGIS-100 prototype use of an existing vertical shaft on the Fermilab site that leads to underground areas: Scientists will perform precision quantum measurements using clouds of ultracold falling atoms, whose phases can be manipulated and read out using lasers, aiding in the test for lightweight dark matter particles. The length of the 100-meter drop expands the current limits of the technology by about a factor of 10 and provides opportunities for significant advances in the systematics of this important technology.
MAGIS-100 combines the unique physical features of the Fermilab site with the laboratory expertise in vacuum and magnetics fields to give a high level of support to the physics collaboration.
High-energy physics applications of quantum computing
Quantum computing has the potential to take on the most formidable calculations in particle physics, calculations that are, it is not an exaggeration to say, otherwise impossible. The Fermilab computing community is now pursuing a program to leverage this powerful technology to solve problems in data analysis and theoretical calculations.
High-energy physicists are not new to devices that operate using quantum hardware systems. For decades, they have been using quantum sensors in particle detectors and quantum devices in particle accelerators. Now physicists are extending this expertise into the realm of quantum software and computing.
The task before the Fermilab computing community is to cast particle physics problems in a way that will make quantum computing beneficial, describing physics systems so that they’re expressible in qubits. Simulations will allow physicists to refine how they cast problems such as those in quantum chromodynamics or in physics beyond the Standard Model into a form amenable to quantum computing. Scientists must then be able to read out the state of the quantum computer and translate the output back into binary — traditional — data to be used in subsequent calculations.
In partnership with the University of Chicago, Fermilab will use vendor-provided, cloud-based computing resources to develop and execute computing algorithms for the future.
Foundational quantum science
The immense processing capacity of quantum computers is opening avenues for physicists to address a whole new class of physics problems, previously rendered insoluble within the limits of classical computing. Theoretical scientists are developing mathematical models that simulate quantum computing systems — and then mapping quantum physics systems onto those models. This process enables scientists to evolve the simulated quantum computing system in a way that’s advantageous for the field of particle physics.
The possibility of solving problems on quantum computers, one first outlined by Richard Feynman in the 1980s, may be realized in the next decade. Quantum science may give scientists a deeper understanding of black holes, space-time and quantum field theory.
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