  Entanglement distillation has many applications in quantum information
processing and is an important tool for improving the quality and efficiency of
quantum communication, cryptography, computing, and simulation. We propose an
entanglement distillation scheme using only one pair of polarization-frequency
hyperentangled photons, which can be equivalently viewed as containing two
pairs of entangled logical qubits: a pair of polarization-entangled qubits and
a pair of frequency-entangled qubits. To perform the required CNOT operation
between the two qubits we consider the use of a polarization-dependent
frequency converter. Compared to past methods of entanglement distillation that
relied on polarization and spatial-mode/energy-time degree of freedom, the
utilization of frequency-encoded qubits offers an advantage in that it is
immune to bit-flip errors when the channel is linear. After distillation, the
fidelity of polarization entanglement can be significantly improved by
sacrificing the frequency degree of freedom. Through simulation, we show that
high fidelity gains, large yield, and high distillation rate can be achieved.
Our distillation scheme is simple to implement with current technologies,
compatible with existing telecommunication fiber networks, and is a promising
approach for achieving efficient quantum communication.
