
5
teraction of the form of Eq. (6) with 1 on the edge and 0
in the bulk, the steady state solution has exponentially
localized edge photon density, with nearly all-to-all edge
correlations, Fig. 3. For a fixed η, these sites will obey a
volume-law scaling in entanglement entropy, [37], where
maximally separated edge sites are now highly entangled,
Fig. 3. Having all edge sites lie on the same topological
boundary is crucial for this to occur [37].
In the limit that η→ηc, the steady state will be dom-
inated by the topological edge modes approaching insta-
bility. Treating the edge as a ring, we can label these by
their momenta k; the steady state has all momenta kand
k+πin a TMS vacuum. Close enough to instability, a
single momentum will dominate, generating uniform edge
photon densities, see Fig. 3(a), and a “checkerboard” of
correlations, see Fig. 3(b). The checkerboard is a result
of the chiral symmetry, which admits only correlations
within a sublattice. The values of the correlations and
densities can be understood directly from Eq. (10), where
hˆni,j i ∼ sinh(rk)2and hˆai,j ˆai0,j0i ∼ sinh(rk) cosh(rk)
are superexponentially enhanced compared to the bulk
modes. This gives an arbitrary amount of entanglement
between any two edge sites on the same sublattice as
η→ηc. This also means that for a relatively weak di-
mensionless pumping (η < 10−3in Fig. 3), the steady
state can still have a large number of photons (O(102) in
Fig. 3), that is completely independent of the strength of
the dissipation κcompared to the Hamiltonian.
Implementation.— The basic master equation is natu-
rally suited for any circuit- or cavity-QED experimental
platform that can generate tunable couplings, along with
an engineered lossy mode. Quantum systems that have
been able to successfully create topological photonic or
phononic lattices span superconducting circuits [50,54],
micropillar polariton cavities [28], photonic cavities [57],
photonic crystals [55], ring resonators [29,30,52,53,58],
and optomechanics [59,60]. In order to generate the
requisite jump operator in Eq. (6), one can couple the
dissipation sites to an auxiliary bosonic mode ˆ
bwith the
interaction
ˆ
HI=gˆ
b†(ˆa0+ηˆa†
1)+H.c.(13)
In the limit that the auxiliary mode ˆ
bis very lossy with
a loss rate κg, this gives the desired jump operator,
with an effective strength Γ = 4g2/κ, [61]. This allows
one to easily engineer the desired reservoir with few ad-
ditional resources.
Conclusions.— We have demonstrated that dissipative
pairing interactions lead to a previously unexplored class
of instabilities in bosonic systems, where stable Hamil-
tonians and stable dissipation combine to give unstable
dynamics. We have shown that these instabilities are
incredibly sensitive to topological boundaries, providing
a new mechanism to selectively excite topological edge
modes without needing any momentum or frequency se-
lectivity. Moreover, the steady state of the dynamics
remains pure all the way up to the instability point, al-
lowing one to populate the edge with an arbitrary number
of zero-temperature excitations. Our ideas are compat-
ible with a variety of different experimental platforms,
and require few resources to implement.
This work is supported by the Air Force Office of Sci-
entific Research under Grant No. FA9550-19-1-0362, and
was partially supported by the University of Chicago Ma-
terials Research Science and Engineering Center, which is
funded by the National Science Foundation under Grant
No. DMR-1420709. A.C. also acknowledges support from
the Simons Foundation through a Simons Investigator
Award (Grant No. 669487, A.C.).
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