Data Qubits Research Articles

Novel quantum information solution to copy-protection and secured authentication

The security of the proposed quantum information data protection system lies in the fundamental difference between classical and quantum information. In the proposed quantum copy-protection system, classical data are stored in the secret rotation angles of non-orthogonal quantum states. The decryption of the stored information is not possible in the classical representation and the decryption mechanism of data qubits is realised by secret unitary rotations. The data protection system uses a quantum-based data storage system and quantum media authentication method to distinguish between original and forged data media. This paper discusses the working mechanism of quantum copy protection and analyses the success probabilities of the quantum probabilistic authentication steps.

Latency in local, two-dimensional, fault-tolerant quantum computing

(pp0666-0682) F.M. Spedalieri and V.P. Roychowdhury We analyze the latency of fault-tolerant quantum computing based on the 9-qubit Bacon-Shor code using a local, two-dimensional architecture. We embed the data qubits in a 7 by 7 array of physical qubits, where the extra qubits are used for ancilla preparation and qubit transportation by means of a SWAP chain. The latency is reduced with respect to a similar implementation using Steane's 7-qubit code~\cite{svore2007a}. Furthermore, the error threshold is also improved to $2.02 \times 10^{-5}$, when memory errors are taken to be one tenth of the gate error rates.

High-Fidelity Quantum Operations on Superconducting Qubits in the Presence of Noise

We present a scheme for implementing quantum operations with superconducting qubits. Our approach uses a "coupler" qubit to mediate a controllable interaction between data qubits, pulse sequences which strongly mitigate the effects of 1/f flux noise, and a high-Q resonator-based local memory. We develop a Monte Carlo simulation technique capable of describing arbitrary noise-induced dephasing and decay, and demonstrate in this system a set of universal gate operations with O(10(-5)) error probabilities in the presence of experimentally measured levels of 1/f noise. We then add relaxation and quantify the decay times required to maintain this error level.

Quantum error correction via robust probe modes

We propose a new scheme for quantum error correction using robust continuous variable probe modes, rather than fragile ancilla qubits, to detect errors without destroying data qubits. The use of such probe modes reduces the required number of expensive qubits in error correction and allows efficient encoding, error detection and error correction. Moreover, the elimination of the need for direct qubit interactions significantly simplifies the construction of quantum circuits. We will illustrate how the approach implements three existing quantum error correcting codes: the 3-qubit bit-flip (phase-flip) code, the Shor code, and an erasure code.

Two-reservoir model of quantum error correction

We consider a two reservoir model of quantum error correction with a hot bath causing errors in the qubits and a cold bath cooling the ancilla qubits to a fiducial state. We consider error correction protocols both with and without measurement of the ancilla state. The error correction acts as a kind of refrigeration process to maintain the data qubits in a low entropy state by periodically moving the entropy to the ancilla qubits and then to the cold reservoir. We quantify the performance of the error correction as a function of the reservoir temperatures and cooling rate by means of the fidelity and the residual entropy of the data qubits. We also make a comparison with the continuous quantum error correction model of Sarovar and Milburn [Phys. Rev. A 72 012306].