Single-Photon Atomic Sorting: Isotope Separation with Maxwell’s Demon M. Jerkins, 1 I. Chavez, 1 U. Even, 2 and M. G. Raizen 1 $^{1}$Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin, Austin, TX 78712 $^{2}$Sackler School of Chemistry, Tel-Aviv University, Tel-Aviv, Israel Isotope separation is one of the grand challenges of modern society and holds great potential for basic science, medicine, energy, and defense. We consider here a new and general approach to isotope separation. The method is based on an irreversible change of the mass-to-magnetic moment ratio of a particular isotope in an atomic beam, followed by a magnetic multipole whose gradients deflect and guide the atoms. The underlying mechanism is a reduction of the entropy of the beam by the information of a single-scattered photon for each atom that is separated. We numerically simulate isotope separation for a range of examples, including lithium, for which we describe the experimental setup we are currently constructing. Simulations of other examples demonstrate this technique’s general applicability to almost the entire periodic table. We show that the efficiency of the process is only limited by the available laser power, since one photon on average enables the separation of one atom. The practical importance of the proposed method is that large-scale isotope separation should be possible, using ordinary inexpensive magnets and the existing technologies of supersonic beams and lasers. PACS numbers: 32.10.Bi The efforts to separate isotopes date back to the 1930’s and fall into several categories. Two standard meth- ods of separation are gaseous diffusion and the ultra- centrifuge [1–3]. These methods require many stages of enrichment and are very inefficient. Furthermore, these methods are only suitable for a few elements that can be kept in gas phase, which is a common limitation of isotope separation schemes [4]. Isotope separation is also accomplished with mass spectrometry [5, 6]. This method has high isotopic selectivity due to the use of a quadrupole mass filter, but it is very inefficient due to the low probability of electron-bombardment ionization and is limited by space-charge. In recent years the method of isotope separation by laser ionization was developed [7]. This approach is highly selective but requires multiple high-powered lasers for efficient ionization. The produc- tion rate is also limited by resonant charge exchange. With this background, it is clear that there is an urgent need for a new and efficient method of isotope separa- tion, the topic of our work. We first provide an overview of the approach and relate it to the historic problem of Maxwell’s Demon. We then analyze several representa- tive cases using available NIST data [8] and provide the results of numerical simulations. Finally we discuss the prospects for scalability and experimental realizations. We start with a generic prototype for isotope sepa- ration: a collimated atomic beam of a single element, composed of multiple isotopes. To be more specific, we consider a three-level atom with an initial ground state | i > , an electronic excited state | e > , and a final state | f > . We further assume that the magnetic moment of state | i > , m i , is different than the magnetic moment of state | f > , m f . Now suppose that an atom crosses a laser beam which induces an irreversible transition from state | i > to state | f > by absorption followed by spontaneous emission. We now discuss a more realistic scenario that we plan to construct in our laboratory. The starting point for this approach must be an atomic beam that has the lowest possible entropy of translational motion. Collimation of an effusive beam is not a viable approach since the re- sulting flux is too small [11]. The best candidate is the supersonic beam, which is generated with a high pres- sure carrier gas expanding through a small aperture [12]. Supersonic beams possess remarkable properties, such as an angular divergence of only a few degrees and a veloc- ity spread that is 1% of the mean velocity [13]. These beams are typically pulsed, but for the purpose of iso- tope separation they should be run continuously to max- imize throughput. The desired element can be entrained into the flow near the output of the nozzle, acquiring the We call this process Single-Photon Atomic Sorting be- cause each atom is sorted by scattering exactly one pho- ton. It is closely related to a one-way barrier for atoms that was used as a general method for cooling the trans- lational motion of atoms [9]. The goal is to lower the entropy of the atomic beam by separating the isotopes. This process can be viewed as a realization of Maxwell’s Demon in the sense proposed by Leo Szilard in 1929. Here the Demon acts as a sorter, sending each isotope in a different direction. The entropy of the beam cannot be lowered with any time-dependent Hamiltonian such as an RF drive [10], and an irreversible step is required. The atom scatters one spontaneous photon from the laser beam, increasing the photon’s entropy. This increase compensates for the decrease in the entropy of the beam. The laser is tuned to one isotope, changing its magnetic moment, while not affecting the others. The atom then passes through a magnetic gradient ∇ B(x), created by a magnetic multipole. The magnetic multipole acts like a filter, guiding only low-field seeking states. arXiv:1001.0944v2 [physics.atom-ph] 7 May 2010