Figure 1

The first scheme for the unidirectional wall. Beam $B$ blue detuned from the resonance creates repulsive potential for atoms in state $|1⟩$. Beam RES is tuned to atomic resonance.Reuse & Permissions

Figure 2

Illustration of the phase compression process. As the unidirectional wall is placed inside of a box, atoms are accumulated in the smaller part, thus increasing the density. Kinetic energy increase is due to photon recoil as atoms decay to the ground state.Reuse & Permissions

Figure 3

(a) Initial and final velocity distributions for parameters $\tau =10$, $l_1=100$, $l_2=10$, and ${\sigma }_v=5$. The thick line shows initial distribution. Total initial number of particles is 50 000. Final distribution is not thermally equilibrated. Dips in it are due to scattering of a single photon. (b) Distribution of times after which particles end up in the smaller region. (c) Change of compression in phase space, with solid line for analytic expression given by analytic formula (2); limiting case (3) is not distinguishable from it in this regime. (d) Average compression rate as the size of the larger region $l_1$ is varied, with $f=0.90$; the lines show the average compression rate estimated from (6) with $f=0.95$. The numerical solution of (5) gives an indistinguishable result in this regime as well. (e) and (f) the same when decay time $\tau$ is varied.Reuse & Permissions

Figure 4

Extension of the scheme in Fig. 1 to a three-level atom. Transition $|1⟩\to |2⟩$ is a strong dipole transition to create a substantial repulsive wall for state $|1⟩$. Level $|3⟩$ is metastable with lifetime comparable to transit time through beams.Reuse & Permissions

Figure 5

Scheme that may be used to create a unidirectional wall for the case of alkali atoms. Beam $M$ is attractive for state $|1⟩$ and repulsive for $|2⟩$. Beam RES transfers atoms from $|1⟩$ to $|2⟩$ in a few scattering events.Reuse & Permissions