PORTLAND, Ore. Future versions of the Internet will store and transfer quantum information--qubits--from node to node, researchers predict. After each operation, an acknowledgement pulse signaling a successful transfer must be sent to insure the smooth interchange of information among network nodes.
Acknowledgement entails inspecting the data values, but that would destroy quantum information. Therefore, MIT scientists have invented a new method of signaling the reception of qubits without revealing their values.
Qubits encode both ones and zeroes simultaneously in what is called a superposition of values that enable calculations to be streamlined by operating on the both values at the same time. According to the Heisenberg Uncertainty Principle, their observation resolves the very ambiguities that make qubits useful.
In the lab, qubit values can be encoded on phonons--vibrations on individual atoms of a super-cold gas, which can perform a quantum calculation, then read out the result, terminating the calculation by resolving the superposition, or "coherence," of the qubit.
The concept of a quantum version of the Internet and other network topologies, entails encoding qubits on many atoms at once--called a magnon. In contrast to a single phonon excitation in a crystal lattice of atoms, the magnon represents a collection of qubits formed as a quantized spin wave.
Magnons behave together as a quasi-particle with a fixed amount of energy and lattice momentum. Unfortunately, such a quantized spin wave has the same limitation as individual qubits: they cannot be inspected without resolving their coherence.
MIT researchers say they have demonstrated a quantum "herald" pulse that acknowledges the transfer of a collection of qubits onto a magnon of atoms without resolving their coherence. The herald pulse does not disturb the qubits states, but does acknowledge their successful transmission to a magnon in the super-cooled atomic gas.
The quantum memory value is received from polarized qubits on incoming photons with the herald pulse acknowledging its successful storage in the cold gas. Later, another photon with the same polarization state as the original is retrieved from the gas, thereby proving that the herald pulse preserved the quantum information by only announcing the successful reception and storage of the qubits without resolving their superposition of quantum values.