In the process, it is doing the once-unlikely, if not unthinkable: using instruments of direct monetary control, thereby violating the policy recommendations that advanced countries have repeatedly made to emerging economies.
To its credit, the BOJ has demonstrated that its tool set isn't empty. But this isn't the key question. Rather, it is whether the central bank can regain policy effectiveness. And here, the initial signs are far from encouraging.
This situation is similar to what happened earlier this year, when the BOJ surprised many and took short-term interest rates to negative levels. The results so far suggest that BOJ policy has not only been ineffective but also potentially counterproductive.
Consider the yen: after an initial depreciation -- what Japanese officials wanted in order to promote growth with higher exports and rising demand for domestic goods to replace imports -- the currency has appreciated. If this holds, the stock market would be inclined to sell-off, thereby erasing Wednesday's gains.
BOJ is undermining its credibility while opening itself up to greater political interference.
Some will suggest that that the BOJ should have done even more to avoid this situation --- for example, by also pushing interest rates even deeper into negative territory by expanding its quantitative easing asset-purchase programs in an aggressive open-ended fashion. I suspect that isn't a good idea.
Based on initial evidence, the BOJ has stumbled into the lose-lose-lose situation that former Federal Reserve Chairman Ben Bernanke in August 2010 called the "benefits-costs-risks" equation for unconventional monetary policies: the benefits are negative; costs, including the unintended consequences, are increasing; and risks are becoming more severe. As a consequence, the BOJ is undermining its credibility while opening itself up to greater political interference.
The Bank of Japan would be much better off, both in the short and longer term, to make its measures conditional on the government moving ahead more decisively with implementing Abe's "third arrow" -- adopting pro-growth structural reforms to make the economy more competitive by promoting equality for women in the workforce, improving corporate governance, reforming labor markets and enhancing fiscal effectiveness.
That is where the focus needs to be, not on extending central bank policy experiments -- in Japan and elsewhere.
El-Erian is chief economic adviser at Allianz, chairman of President Obama's Global Development Council and former chief executive officer and co-chief investment officer of Pimco.