Quantum Information Control Research Articles

Autonomous Estimation of High-Dimensional Coulomb Diamonds from Sparse Measurements

Quantum dot arrays possess ground states governed by Coulomb energies, utilized prominently by singly occupied quantum dots, each implementing a spin qubit. For such quantum processors, the controlled transitions between ground states are of operational significance, as these allow the control of quantum information within the array such as qubit initialization and entangling gates. For few-dot arrays, ground states are traditionally mapped out by performing dense raster-scan measurements in control-voltage space. These become impractical for larger arrays due to the large number of measurements needed to sample the high-dimensional gate-voltage hypercube and the comparatively little information extracted. We develop a hardware-triggered detection method based on reflectometry, to acquire measurements directly corresponding to transitions between ground states. These measurements are distributed sparsely within the high-dimensional voltage space by executing line searches proposed by a learning algorithm. Our autonomous software-hardware algorithm accurately estimates the polytope of Coulomb blockade boundaries, experimentally demonstrated in a 2$\times$2 array of silicon quantum dots.

Encryption, decryption, and control with fractional quantum bits, quantum chiral states and pyramidal quantum bits switching in graphene

A novel method for encryption, decryption, and control of data using the theory of “rings and fields” is proposed. A system comprising a ring or loop with a maximum of six vector tuples or sub-loops, which are changed into knots on a ring, is suggested, whereby these vector tuples at 0.4 ≤ nf ≤ 0.9 hold Dirac bosons. The Dirac bosons are precessed at characteristic frequencies and are integrated with a braid; the remaining fractional quantum bits (f-qubits) are occupied with Dirac fermions with the same braid, i.e., 0.1 ≤ nf ≤ 0.3. The fractional Fourier transform is used for modeling and simulating the eigenfunctions for stretching, twisting, and twigging. The fractional charges are quantized and invariant at knots, where subquanta—Dirac bosons—are held on the honeycomb lattice of graphene. The degeneracy of f-qubits is permanently established. The characteristic magnetic excitations due to different precessing frequencies of Dirac bosons are exploited for encryption and decryption. The spinning and precessing Dirac fermions are used for pyramidal switching. Addresses for f-qubits are evaluated by normalizing the Hamiltonian operator, which becomes Hermitian. The topological transitions for a quantized non-interacting electron as above are exploited. A method for encryption, decryption, and control of quantum information with seventy-two (72) “quantum chiral states” is suggested with graphene. The chiral matrix of nfxg2/ℏc, where 0.1 ≤ nf ≤ 0.9 and 0.02 ≤ g2/ℏc ≤ 0.08, is the most suitable option for f-qubits as compared to qubits especially when conformal mapping for quantum computation is accomplished.

Quantum information processing using quasiclassical electromagnetic interactions between qubits and electrical resonators

Electrical resonators are widely used in quantum information processing, by engineering an electromagnetic interaction with qubits based on real or virtual exchange of microwave photons. This interaction relies on strong coupling between the qubits' transition dipole moments and the vacuum fluctuations of the resonator in the same manner as cavity quantum electrodynamics (QED), and has consequently come to be called ‘circuit QED’ (cQED). Great strides in the control of quantum information have already been made experimentally using this idea. However, the central role played by photon exchange induced by quantum fluctuations in cQED does result in some characteristic limitations. In this paper, we discuss an alternative method for coupling qubits electromagnetically via a resonator, in which no photons are exchanged, and where the resonator need not have strong quantum fluctuations. Instead, the interaction can be viewed in terms of classical, effective ‘forces’ exerted by the qubits on the resonator, and the resulting resonator dynamics used to produce qubit entanglement are purely classical in nature. We show how this type of interaction is similar to that encountered in the manipulation of atomic ion qubits, and we exploit this analogy to construct two-qubit entangling operations that are largely insensitive to thermal or other noise in the resonator, and to its quality factor. These operations are also extensible to larger numbers of qubits, allowing interactions to be selectively generated among any desired subset of those coupled to a single resonator. Our proposal is potentially applicable to a variety of physical qubit modalities, including superconducting and semiconducting solid-state qubits, trapped molecular ions, and possibly even electron spins in solids.

Geometric Factors in Electromagnetic Field Commutators and the Quantum Information Control of Vacuum Fluctuations

The electromagnetic field commutation relations are defined in terms of geometric factors that are double averages over two finite four-dimensional space-time regions. The square root of any of the uncertainty relations derived from the aforementioned commutators is taken as a critical field, in the sense that any electromagnetic field much larger than it can be treated as classical. Another critical electromagnetic field associated with the quantum information control of vacuum fluctuations can be chosen as the square root of the mean quadratic fluctuation of each quantity of electromagnetic field, when the number of photons is defined and is equal to zero. Any electromagnetic field expectation value could be measured if it is much greater than the last critical field. This article covers a magnitude order comparison between the critical fields and its consequences for measuring the electromagnetic field information.