Frontiers of Engineered Coherent Matter and Systems Proceedings of a Workshop (2025) / Chapter Skim
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Pages 45-59
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From page 45... ...
This is a much easier measurement to perform, he continued, than other measurements done in, for instance, cold atom systems with degenerate gasses that would offer similar insights into the BCS gap energy U Next, Thompson described another way that this emulation of BCS super conductors with atoms in an optical cavity has been used to study superconductivity.
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From page 46... ...
. "When I build a quantum sensor of time, of acceleration, of rotation, of magnetic field, of the electric field, that's what we're sensing," he said.
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From page 47... ...
They can get a factor of about 60 beyond the standard quantum limit by using an ensemble of 1 million atoms (Cox et al. 2016; Hosten et al.
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From page 48... ...
"That's the first time that's ever been achieved," he said, "so we think this is a real milestone." Collective Recoil Mechanism Noting that he had been focusing on spin degrees of freedom and interactions between spin states, Thompson said it is also possible to get interactions between momentum states. In particular, if 2 qubit states are two different momentum states, then it is possible to use lasers to induce a scattering event into the cavity that will cause the atoms to flip their momentum states.
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From page 49... ...
After the presentation, Toor asked how the work Thompson described could be used for quantum computation. He answered that he is not in the computation field -- he is interested in quantum simulation and quantum sensing -- and he does not believe that the optical cavities he works with are well suited for quantum computation.
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From page 50... ...
Fiber transmission has a lot of signal loss, Peters noted, but it has a major advantage that the optical fibers can be curved rather than requiring the commu nication to follow a straight line, so that "we can bend it around any place we want and get our photons to locations where we can put our quantum repeater stations." It is more difficult in free space, such as going from a low Earth-orbit satellite to the ground, he said, because repeater stations will probably not be installed between the two. "It's possible, but not super likely." Going into further detail about the difficulties posed by signal loss, Peters first mentioned the no-cloning theorem, which says that it is not possible to just boost the quantum signal.
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From page 51... ...
In designing quantum networks, one must not only deal with the quantum issues but also figure out how to make things work. "You have to look at the other physical constraints as well as the engineer ing constraints and how they impact your ability to do the quantum part of the protocol," he said.
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From page 52... ...
One possible way to address the issue with linear optical operations, Peters said, is to use what he called a linear optical frequency processor, noting that the steps taken to enable fault-tolerant quantum networking are pretty much the same as what is needed to enable linear optical quantum computing. The approach they use starts with a system where they define their logical qubit in two different fre quency modes of light.
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From page 53... ...
' and it's a little harder to answer that than you might at first think." In addressing the issue of putting quantum signals on existing fiber optic lines, Peters and his team first approached it in the context of quantum key distribution (QKD)
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From page 54... ...
However, he con tinued, because they can manipulate that frequency degree of freedom directly by using the linear optical gates, they think that they can turn something that has been a challenge into something they can use to make the problem easier to address. As an aside, Peters showed a photo of the quantum network test bed at the Oak Ridge National Laboratory and said that the test bed has recently installed a long fiber network that allows them to test systems up to 300 km in length.
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From page 55... ...
After the presentation, Thompson asked Peters about the thinking in the quantum networking community about using local quantum networks with local interconnects versus long-distance applications. "The idea," Peters replied, "is that if I have things that are sitting next to each other, maybe I don't have to pick a wavelength that goes down an optical fiber, because my optical fiber will be so short I can pick whatever wavelength I want.
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From page 56... ...
He first became inter ested in the field because of a 1998 paper by Jaksch and colleagues that modeled a transition from a superfluid to a Mott insulator in an optical lattice containing an ultracold dilute gas of bosonic atoms. The field has grown in the intervening years, and now a wide variety of quantum simulations have been studied across a number of different platforms, including ion traps, optical lattices, Rydberg tweezers, and superconducting devices.
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From page 57... ...
"You have a many-body wave function as a super position of different configurations," he said, and the quantum simulators make it possible to repeat an experiment thousands of times, measuring the configuration each time. This produces a probability distribution of configurations, which allows researchers to calculate "multi-point correlation functions that are simply inacces sible in real condensed matter materials," he said.
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From page 58... ...
Concerning where the field of equilibrium quantum simulations currently stands, Bloch said that it is now entering a new phase, and the next few years should see experiments pushing into the so-called pseudo-gap regime with very compli cated questions to answer. "What is amazing now with the quantum simulation ap proaches," he said, "is that we can combine macroscopic thermodynamic quantities from material science and putting microscopic, real-space measurements beneath that, revealing hidden orders, multi-point correlation functions, and fluctuations in these systems." Connecting the microscopic picture with macroscopic quantities will open a whole new and exciting research direction in the future, he predicted.
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From page 59... ...
Currently many people are pursuing the digital model of quantum computing, while others are exploring the analog model of quantum simulation, and perhaps, he said, the ideal would be to apply the best of both worlds. That is, researchers can harness the very long coherence times and coherent evolution found in analog quantum simulation but combine that with the very powerful digital readout of preparation methods.
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