Heat-bath cooling of spins in two amino acids

Abstract

Heat-bath cooling is a component of practicable algorithmic cooling of spins, an approach which might be useful for in vivo 13 C spectroscopy, in particular for prolonged metabolic processes where substrates that are hyperpolarized ex-vivo are not effective. We applied heat-bath cooling to 1,2-13 C 2 -amino acids, using the α protons to shift entropy from selected carbons to the environment. For glutamate and glycine, both carbons were cooled by about 2.5-fold, and in other experiments the polarization of C1 nearly doubled while all other spins had equilibrium polarization, indicating reduction in total entropy. The effect of adding Magnevist R , a gadolinium contrast agent, on heat-bath cooling of glutamate was investigated.

Achievable Polarization for Heat-Bath Algorithmic Cooling

“…Based on this work, many cooling algorithms have been designed [6][7][8][9][10][11]. HBAC is not only of theoretical interest, experiments have already demonstrated an improvement in polarization using this protocol with a few qubits [12][13][14][15][16][17][18], where a few rounds of HBAC were reached; and some studies have even included the impact of noise [19].…”

“…Based on this work, many cooling algorithms have been designed [6][7][8][9][10][11]. HBAC is not only of theoretical interest, experiments have already demonstrated an improvement in polarization using this protocol with a few qubits [12][13][14][15][16][17][18], where a few rounds of HBAC were reached; and some studies have even included the impact of noise [19].Through numerical simulations, Moussa [7] and Schulman et al [8] observed that if the polarization of the bath ( b ) is much smaller than 2 −n , where n is the number of qubits used, the asymptotic polarization reached will be ∼ 2 n−2 b ; but when b is greater than 2 −n , a polarization of order one can be reached. Inspired also by the work of Patange [20], who investigated the use of algorithmic cooling on spins bigger than 1 2 (using NV center where the defect has an effective spin 1), we investigate the case of cooling a qubit using a general spin l, and extra qubits which get contact with a bath.…”

Algorithmic cooling in liquid-state nuclear magnetic resonance

“…We bypassed Shannon's bound in three different processes. The current optimal control methods (GRAPE), and better ones such as a second order GRAPE [42] and Krotov based optimization [43] could enable various applications of AC in magnetic resonance spectroscopy [13,14,44] and maybe also other potential applications [45][46][47][48][49][50][51][52][53][54]. ln (4) (see [23]), where ε C,eq is the carbons' equilibrium polarization.…”

“…On the one hand, it was originally suggested as a method for increasing the qubits' purification level [5][6][7][8][9][10], as qubits in a highly pure state are required both for initialization and for fault tolerant [11,12] quantum computing. On the other hand, the suggested novel usage of data compression may potentially be found useful for increasing the signal to noise ratio of liquid-state NMR and in vivo magnetic resonance spectroscopy [6,13,14].…”

“…In such scenarios, even a special case -AC without compression (called heat bath cooling [14,23]), can cool the spin system beyond Shannon's bound. This can be done by applying a polarization transfer [31] from the proton to C1, or alternatively, by swapping the two polarizations via a polarization exchange (PE) gate, and waiting for the proton to regain some of its polarization (while the carbon is still cool).…”