Effect of diatomic molecular properties on binary laser pulse optimizations of quantum gate operations

We present a systematic approach to implementation of basic quantum logic gates operating on polar molecules in pendular states as qubits for a quantum computer. A static electric field prevents quenching of the dipole moments by rotation, thereby creating the pendular states; also, the field gradient enables distinguishing among qubit sites. Multi-target optimal control theory is used as a means of optimizing the initial-to-target transition probability via a laser field. We give detailed calculations for the SrO molecule, a favorite candidate for proposed quantum computers. Our simulation results indicate that NOT, Hadamard and CNOT gates can be realized with high fidelity, as high as 0.985, for such pendular qubit states.

Section: At Present It Remains An Open Question Whether In the Presmentioning

confidence: 99%

Implementation of quantum logic gates using polar molecules in pendular states

Zhu¹,

Kais²,

Qi³

et al. 2013

“…The majority of theoretical studies within diatomic quantum computing, using shaped laser pulses, produce excellent qubit control but with laser pulses that are difficult, or perhaps impossible, to realize experimentally and/or only show proof of principle applications on a particular choice of diatomic molecule. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] In contrast, we previously studied the performance of shaped laser pulses on a general model diatomic 31 and the ability to achieve high control with laser pulses having very few parameters (binary pulse shaping). 32 The theoretical optimizing or shaping of laser pulses generally comes in two forms: optimal control theory (OCT) 33,34 and genetic algorithm (GA) 11 optimization.…”

Section: Introductionmentioning

confidence: 99%

“…[35][36][37] On the other hand, the GA can be incorporated into an experimental closed-loop feedback setup and thus theoretical implementation allows for an appropriate description of the possible laser pulses shapes. While the molecular structure is clearly important, 31 it is also necessary to explore the limitations of the laser pulse shaping apparatus within the context of this specific application.…”

Section: Introductionmentioning

confidence: 99%

“…We have implemented an analogous theoretical framework, which was also used in our previous works. 31,32 The object of the study detailed herein is to elucidate the importance of some adjustable parameters within a typical LC-SLM, namely (i) the effect of varying the LC-SLM pixel frequency resolution (dν), (ii) effective variance of the amplitude (A j ), (iii) phase (φ j ) at each pixel, and (iv) the effect of changing the number of pixels (n) included within the laser pulse shaping. Each of these four important parameters affects the total number of laser pulse combinations and thus the total size of the parameter space that needs to be explored to find the optimal laser pulse.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of laser pulse shaping parameters on the fidelity of quantum logic gates

Zaari

Brown

2012

Self Cite

The effect of varying parameters specific to laser pulse shaping instruments on resulting fidelities for the ACNOT(1), NOT(2), and Hadamard(2) quantum logic gates are studied for the diatomic molecule (12)C(16)O. These parameters include varying the frequency resolution, adjusting the number of frequency components and also varying the amplitude and phase at each frequency component. A time domain analytic form of the original discretized frequency domain laser pulse function is derived, providing a useful means to infer the resulting pulse shape through variations to the aforementioned parameters. We show that amplitude variation at each frequency component is a crucial requirement for optimal laser pulse shaping, whereas phase variation provides minimal contribution. We also show that high fidelity laser pulses are dependent upon the frequency resolution and increasing the number of frequency components provides only a small incremental improvement to quantum gate fidelity. Analysis through use of the pulse area theorem confirms the resulting population dynamics for one or two frequency high fidelity laser pulses and implies similar dynamics for more complex laser pulse shapes. The ability to produce high fidelity laser pulses that provide both population control and global phase alignment is attributed greatly to the natural evolution phase alignment of the qubits involved within the quantum logic gate operation.

“…There are a number of applications of OCT ranging from the control of chemical reactions 3,17 to quantum optical problems, such as quantum information processing [18][19][20] or the preparation of cold molecules. 21,22 However, the number of theoretical studies where high quality potential energy surfaces including realistic transition dipole moment surfaces are employed is quite limited.…”

Section: Introductionmentioning

confidence: 99%

A theoretical investigation of the feasibility of Tannor-Rice type control: Application to selective bond breakage in gas-phase dihalomethanes

Shu

Rozgonyi

González

et al. 2012

Within the $\tilde {\rm B}$B̃ absorption band of CH2BrCl, we theoretically analyze the laser-induced control of the Br/Cl branching ratio, Br + CH2Cl ← CH2BrCl → CH2Br + Cl, with CH2BrCl initially in its vibrational ground state. For weak-field excitation, the Br/Cl branching ratio increases as a function of wavelength, however, for wavelengths below 180 nm the branching ratio cannot be made smaller than 0.4. Using optimal control theory, we show that the branching ratio can be made significantly less than 0.4, only when very strong fields are employed. Thus, the present work strongly suggests that a Tannor-Rice type laser control mechanism for selective bond breakage in CH2BrCl cannot take place without accompanying photoionization.